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The secondary eye pathway of jumping spiders is complex compared to other spiders (Long 2019). Of interest for me are the optical glomeruli of the secondary eye medulla. Information from the secondary eyes is sent to the lamina, followed by the medulla. From the medulla, nerves project and combine in the mushroom body (Strausfeld et al. 1993). Unlike the mushroom body in insects, it is likely that the mushroom body in spiders is completely given over to vision. In insects, information from the lamina is passed to the medulla via a complete chiasma and this retains a panoramic field of view. In spiders, information from the lamina is chunked in the medulla before being passed to the mushroom body (Strausfeld, 2012). This prevents a panoramic view but may increase the spider's ability to quickly process motion information in discrete regions of the visual field. This may be particularly important for targeting the movement of the principal eyes. Retinotopic information from the lamina is passed to the protocerebrum simultaneously via a separate tract (Strausfeld, 2012). 

The visual systems of different spider families can be correlated to their life histories and behaviors. Many diurnal cursorial spiders like salticids have enlarged principal eyes and small secondary eyes with a wide field of view for detecting prey. Nocturnal hunters like wolf spiders (Family Lycosidae) and net-casting spiders (Family Deinopidae) have small principal eyes and enlarged secondary eyes. Meanwhile, some ambush predators like crab spiders (Family Thomisidae) and web-building spiders like long-jawed orb weavers (Family Tetragnathidae) tend to have small, evenly spaced principal and secondary eyes. Furthermore, the visual processing pathway is separate for the principal and secondary eyes. And the principal and secondary eyes each have their own neural pathway within the spider brain (Strausfeld and Barth, 1993). 

The number, complexity, and arrangement of spider eyes vary across spider families and often correlate with behavior. In addition, the size and organization of the visual processing regions of the protocerebrum also vary (Long 2019). The structural and functional unit of the nervous system of spiders, like other animals, is a neuron. Additionally, the spider central nervous system is composed of discrete synaptic regions called neuropils and the inside of the neuropil is comprised of nerve fibers and glial components. The central nervous system of spiders is composed of two major regions called the supra-esophageal and sub-esophageal regions (Barth 2002; Strausfeld 2012). The supra-esophageal region is considered to be the brain of the spider and it consists of the protocerebrum and the deutocerebrum. The sub-esophageal region is comprised of tritocerebrum and leg ganglia (Strausfeld 2012). In addition, the sub-esophageal region contains afferents from all sensory systems except the eyes (Barth, 2002; Strausfeld, 2012). Moreover, this is the largest region of the spider central nervous system. For example, in Cupiennius salei, the sub-esophageal region makes up about 85% of the total central nervous system (Barth, 2002). The protocerebrum contains the optical lobes that receive information from the spider’s eyes. Among them, the most important are structures called the central body, proto-cerebral bridge and paired mushroom bodies. All of them receive information from various sensory and motor cells. The input of information into the protocerebrum from the rest of the central nervous system supports the idea that it serves as an integration center (Babu and Barth, 1984).

The study of the nervous system of spiders has long been one of the central problems of natural science. The birth of studying the spider central nervous system is dated back to 1890, the year that the brilliant work of Saint Remy laid its foundations. His work described the central nervous system of the labidognath family of spiders (Remy 1890). Moreover, in the 1920s, Hanström applied the Golgi staining technique to study the spider brain. He noticed that spider visual neuropils varied greatly in size and organization (Hanström 1921). Furthermore, Hanström claimed that the spider brain and insect brain have shared neural structures. This idea of brain homology can still be found in current literature today (Babu 1965, Bullock and Horridge 1965, Firstman 1954, Legendre 1959). In addition, Legendre has given a comprehensive study of the brain morphology and development of spiders (Legendre 1965). However, early 20th century researchers, such as SaintRemy, Hanström, and Legendre were limited by techniques and sample quality (Long 2019). 

The seed coat plays an important role in the growth, germination, and protection of the seed. In some plants, there is some evidence that the seed coat might inhibit the seed’s germination. Our study investigated whether the removal of the seed coat impacted the seed germination time. 

We studied 6 species:

• Whole green peas

• Barley

• Chickpeas

• Pinto beans 

• Baby lima beans 

• Green split beans

• Their seed coats were removed using an exacto knife and soaked in water for 1 hour. The seeds were then divided into groups, including the unremoved coat, which is the control. Finally, the seeds were checked every 12 hours and the state of the seeds was recorded.

A graph showing the germination of half the seeds over time shows that many seeds germinated slower without a coating. Time When Over Half of the Seeds Germinated. Comparison of the time when half of the seeds germinated. For barley, baby lima beans, and green split beans, intact seed coats germinated faster. Possible future experiments may lead towards figuring out how optimal germination rates vary by seed species.

The principal and AL eyes may also work together to gather visual information. A recent study (Jakob et al., 2018) investigated how lateral eyes direct the principal eyes of jumping spiders when tracking objects. In order to test this,Phidippus audax spiders were tethered in front of an eyetracker that recorded the gaze direction of the principal eyes. Visual stimuli of different shapes and movement speeds were presented before and after masking the ALEs with removable paint. When unmasked spiders were shown a moving disk, the principal eye retinas moved close together and were able to track it. Meanwhile, spiders with their AL eyes masked were unable to track moving objects, with their principal eye retinas remaining further apart and reacting only briefly when the objects crossed their field of view. However, when the spiders were presented with a motionless object that appeared in the center of the principal eye’s field of view, they actively scanned it regardless of whether the secondary eyes were masked or unmasked. This indicates that masking the secondary eyes does not prevent the principal eyes from investigating stationary objects, but they are needed for targeting stimuli outside of the principal eye’s field of view (Jakob et al., 2018). The integration between principal and secondary eyes has also been studied in Cupiennius salei (Family Ctenidae). The principal eyes of ctenids are moveable, but they are controlled by four muscles instead of six as in jumping spiders (Kaps, 1996) (Land, 1969). Thus, they are not able to engage in complex movements such as torsion. When spiders had their principal eyes masked, they maintained the same eye muscle activity, but masking the secondary eyes reduced principal eye movement (Neuhofer et al., 2009). The researchers concluded that the secondary eyes of C. salei are involved in movement detection, while the principal eyes require input from the secondary eyes to move normally.

To facilitate handling, I placed the spider in a vial to rest in the freezer for 5-8 minutes, with frequent checks to make sure the spider was alive. I then removed the spider from the freezer and gently took it out of the vial using a brush. Next, I placed the spider on the center of a stretched-out piece of Parafilm. To enclose the spider, I folded the Parafilm over it and applied pressure around the spider. Then I carefully punctured the resulting air bubble with a pin, making sure that the spider remained unharmed. 

I placed the tightly wrapped spider over a sectioned quarter of a Styrofoam ball, so that it was centered on the curved surface. In order to secure it to the Styrofoam ball, I applied pressure over the extra Parafilm. With a pin, I then carefully removed the Parafilm over the spider’s head to reveal all its eyes, without exposing the spider’s chelicerae (Figure 5).

The following species were used in the trials (Figure 3): Xysticussp. and Mecaphesa celer (Thomisidae),Cheiracanthium inclusum(Eutichuridae, Ramírez, 2014), and Phidippus princeps. Phidippus princepsis an active diurnal hunter from the Salticidae family with high visual acuity, and was tested to confirm if the experimental set up provided the same results as those obtained by Jakob et al.(2018) using an eyetracker. Cheiracanthium inclusumis an active nocturnal hunter and has eight eyes evenly arranged in two rows of four. Xysticus sp.and M. celerare members of the family Thomisidae, characterized for being diurnal ambush predators that hunt pollinators in flowers. The principal eyes of Misumena vatia, another Thomisidae with a similar eye arrangement, overlap entirely with one pair of secondary eyes (the ALEs), and partially with the rest of secondary eyes (Insausti et al. 2011). The principal eye retinas of M. vatia are equipped with two muscles arranged similarly to those of C. salei(Insausti et al. 2011). The principal eyes of M. vatia have a wider field of view (Insausti et al. 2011) than those of jumping spiders. In thomisids, the PMEs look upwards for aiding in the detection of aerial prey like bees.  

A recent review (Morehouse et al., 2017) compiling the current knowledge on the evolution and molecular foundations of spider vision remarked on the need for further research in this area of investigation. While there is great variation regarding eye arrangements and visual systems across families, most studies on visual behavior have focused on spiders that have similar foraging strategies and do not represent the full range of spider visual morphology or behavior.

The visual systems of different spider families can be correlated to their life histories and behaviors. Many diurnal cursorial spiders like salticids possess enlarged principal eyes and use their secondary eyes to give them wide peripheral vision for detecting prey. Nocturnal hunters like wolf spiders (Family Lycosidae) and net-casting spiders (Family Deinopidae) have small principal eyes and enlarged secondary eyes. Meanwhile, some ambush predators like crab spiders (Family Thomisidae) and web-building spiders like long-jawed orb weavers (Family Tetragnathidae) tend to have small, evenly spaced eyes with little size difference between the principal and secondary eyes.

The principal and AL eyes may also work together to gather visual information. A recent study (Jakob et al., 2018) investigated how lateral eyes direct the principal eyes of jumping spiders when tracking objects. In order to test this,Phidippus audax spiders were tethered in front of an eyetracker that recorded the gaze direction of the principal eyes. Visual stimuli of different shapes and movement speeds were presented before and after masking the ALEs with removable paint. When unmasked spiders were shown a moving disk, the principal eye retinas moved close together and were able to track it. Meanwhile, spiders with their AL eyes masked were unable to track moving objects, with their principal eye retinas remaining further apart and reacting only briefly when the objects crossed their field of view. However, when the spiders were presented with a motionless object that appeared in the center of the principal eye’s field of view, they actively scanned it regardless of whether the secondary eyes were masked or unmasked. This indicates that masking the secondary eyes does not prevent the principal eyes from investigating stationary objects, but they are needed for targeting stimuli outside of the principal eye’s field of view (Jakob et al., 2018). The integration between principal and secondary eyes has also been studied in Cupiennius salei (Family Ctenidae). The principal eyes of ctenids are moveable, but they are controlled by four muscles instead of six as in jumping spiders (Kaps, 1996) (Land, 1969). Thus, they are not able to engage in complex movements such as torsion. When spiders had their principal eyes masked, they maintained the same eye muscle activity, but masking the secondary eyes reduced principal eye movement (Neuhofer et al., 2009). The researchers concluded that the secondary eyes of C. salei are involved in movement detection, while the principal eyes require input from the secondary eyes to move normally.