316 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



that each cell with its thickened walls is a separate structure, and that 

 the deceptive appearance of a network is caused by the close apposition 

 of the thick walls of adjacent cells. This is, of course, what we would 

 expect reasoning from analogy with the rod cells of other eyes. 



In the same figures is noticed the protoplasmic core of each rod cell, 

 which penetrates clear to the extremity of the thick -walled end of the 

 cell. Within these protoplasmic cores are seen here and there (Fig. 3) 

 round, or slightly oval, homogeneous, deeply staining bodies somewhat 

 resembling nuclei. 1 These are found only in the thick-walled ends of the 

 cells, and each cell contains one of them. They seem not to be true 

 nuclei, but to correspond to the very similar bodies found in the rod cells 

 of the eyes of other animals, e. g., the pycnogonids (Morgan), insects 

 ("secondary nuclei," Patten), scorpions (Lankester and Bourne), and 

 probably also to the refractive globules in the cones of the retina of birds. 



The Two Pairs of Smaller Eyes. 



The four smaller eyes of the chain-form of Cyclosalpa pinnata are 

 arranged in two pairs, one pair lying on the posterior face of the gang- 

 lion on each side of the middle line, the other pair lying just below the 

 posterior ends of the two posterior limbs of the unpaired dorsal eye. 

 Fig. 8, Plate XLIX, which represents part of a longitudinal, vertical sec- 

 tion of the ganglion, shows one of each pair of smaller eyes, ex and ey. 

 Fig. 1, Plate LI, a vertical cross-section of the ganglion, shows the two 

 eyes of the posterior pair. They lie imbedded in the midst of the 

 smaller cells of the ganglion, just dorsal to the zone of origin of the 

 nerves that arise from the brain. These eyes consist simply of rod cells 

 which exactly resemble, except in size, the rod cells of the large dorsal 

 eye. These cells are arranged in a hemisphere with their thin-walled, 

 lightly staining ends posterior and their thick- walled, deeply staining 

 ends toward the center of the ganglion. The membrane of the posterior 

 face of the ganglion touches the posterior ends of the rod cells. In the 

 specimens studied, all of which were hardened in acid reagents, no pig- 

 ment was found in the region of these eyes. In the live cyclosalpa it 

 may be that certain of the ganglion cells near the base of the rods are 

 lightly pigmented ; but this pigmentation cannot be very decided, for if 

 ever present in the specimens studied, it had been dissolved by the same 



1 In the figure they are represented as granular. They should be homogeneous, 

 staining a little less deeply than the cell walls. 



