ETTPAGURTTS. 537 



border of " stit'tohen," and it is probable, though not 

 certain, that the nerve fibrillae, passing through the 

 retinular cells from the optic nerve, communicate with 

 them. At the distal end of the rhabdonie is a pear-shaped 

 cavity, first described by Parker, filled with a coagulable 

 fluid (fig. 33). 



(5) Irregular cells, lightly pigmented, are found at 

 "the base of the rhabdome and on both sides of the 

 basement membrane. Parker, who calls them accessory 

 cells, thinks they are probably mesodermic. The nerves 

 from the ommatidia pass into a mass of nervous tissue, 

 underneath the retina, which contains four successive 

 ganglia, and thence to the brain.* 



Various observers have given conflicting accounts of 

 the type of image which is thrown on the retina of the 

 Arthropod eye. From the most recent researches, 

 however, there is little doubt that the image in the 

 compound eye is a single upright one for the whole 

 retina, whose perceptive elements, the rhabdomes, receive 

 each a single impression. Parker has succeeded in 

 obtaining all the results of previous observers by 

 preparing the eye in different ways, and by pointing out 

 where they failed has practically proved that each 

 ommatidium does not receive a small complete image. 



The Otocyst (figs. 35 and 36). 



The otocyst or auditory sac is situated in the 

 proximal joint of the first antenna. There is a small 

 bulbous prominence on the outside of the joint in which 

 it lies, and it opens to the exterior by a narrow 



* The classic paper on the Arthropod eye is by Parker in the 

 Bull. Mus. Camp. AnaL, Harvard, Vol. XXI, p. 45. In details of finer 

 histological work it has been superseded by Parkers further paper in 

 Mitt. a.d. Zool. Stat. z. Neapel, T. XII., 1897, and by Hesse's in Ze.it. 

 Wiss. Zool. Wien., Bd. LXX., p. 347. 



