M. M. METCALF ON THE EYES AND SUBNEURAL GLAND OF SALPA. 321 



ture Cyclosalpa pinnata (Fig. 9, Plate XLVIII). There are seen two 

 portions of the eye, corresponding to the larger and smaller portions 

 of the eye of Cyclosalpa pinnata. The two parts, however, are not so 

 distinct as in that species. Instead of being bound together by a few 

 spindle-shaped cells connecting the pigment layer of the one with that of 

 the other, they are connected by a considerable mass of cells, all of which 

 are pigmented and serve as the pigment layer for both portions of the 

 eye. A comparison of Fig. 2, Plate LIII, with Figs. 6 and 9, Plate 

 XLVIII, will show that the adult Cyclosalpa chamissonis has, in this 

 respect, retained the condition found in the immature Cyclosalpa pin- 

 nata. A comparison of Fig. 1, Plate LIII, with Fig. 2, Plate XLVIII, 

 and Fig. 5, Plate XLIX, will show, also, that there are in Cyclosalpa 

 chamissonis no distinct posterior limbs of the eye, but that this portion 

 is an undivided, continuous structure, retaining the condition found 

 in the eye of the immature chain Cyclosalpa pinnata. The relative 

 arrangement of the histological elements in the three regions of the eye 

 (e', e", e'"}, and also the histological structure and the innervation, are the 

 same in both species ; except that the rod cells are shorter in the posterior 

 part of the eye of Cyclosalpa chamissonis. The histological structure of 

 the dorsal eye of the chain form of the latter species corresponds, then, 

 to the condition found in the adult Cyclosalpa pinnata, while the position 

 and form of the eye correspond to that found in the immature Cyclosalpa 

 pinnata. The unpaired dorsal eye of Cyclosalpa pinnata passes through a 

 chamissonis stage. The marked similarity in form, structure and position 

 of this eye in the two species makes it certain that, in the course of its 

 development, the dorsal eye of the chain Cyclosalpa chamissonis under- 

 goes a shifting of position similar to that described for Cyclosalpa pin- 

 nata, so that in each of these species the anterior end of the eye was 

 primitively posterior, and vice versa. 



The two pairs of smaller eyes found in the chain form of Cyclosalpa 

 pinnata are represented in the chain form of Cyclosalpa chamissonis by 

 two pairs of small eyes with the same form and structure and nearly 

 the same position as in Cyclosalpa pinnata ; the posterior pair being a 

 little more dorsal than in the latter species. 



The structure of the eye in these two species confirms the conclusion 

 drawn from other anatomical resemblances, that the two are closely 

 related, Cyclosalpa chamissonis being the more primitive, and that they 

 are somewhat removed from the other salpidas. 



