126 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



The gut, in the aggregated as in the solitary form, is a close coil, 

 but one can readily trace the course of the intestine, except that the 

 overlying test is usually very dense and somewhat opaque. 



In no species of Salpidae is the pocket valve structure of the lower 

 lip clearer than in the aggregated Thetys vagina. 



The aggregated form of Thetys vagina has a large dorsal eye and 

 two large masses of optic cells in the ganglion (fig. 118), in all of 

 which the rod cells are irregularly polyhedral in shape, not elongated, 

 and their walls are unevenly thickened to form the rod-like materials 

 In the large dorsal eye, two portions may be distinguished, a basal 

 portion with pigment ventral to the rod cells, and an apical portion 

 whose pigment is dorsal to the rod cells, thus showing resemblance to 

 the eye in the true Salpae, except for the degenerate condition of the 



as.-- 



Fio. 118.— Thetys vagina, aggregated form, sagittal section of ganglion, dorsal eye, and 



NEURAL GLAND. X 98 DIAMETERS. FROM MKTCALF (1893, C). 



rod cells in Thetys. The eye of Thetys is short and compact, as in 

 Iasis zonaria, (figs. 101 and 102, p. 108), and the pigment layers of its 

 basal and apical portions are continuous at the sides of the eye but 

 not on the mid-ventral line. The section figured is parasagittal, not 

 sagittal, and shows the pigment of the two regions continuous. 



In the ganglion are two large masses of irregular rod cells, as indi- 

 cated by the rod-like material of which their unevenly thickened wall, 

 are composed. The larger of these masses covers the whole postero- 

 ventral face of the ganglion and is probably homologous with the 

 posterior pair of smaller eyes in the ganglion of Cyclosalpa pinnata. 

 In the interior of the ganglion, below its antero-dorsal surface, is a 

 considerable mass of similar irregular rod cells and just dorsal to 



