vol. 2, pt. 2.] A TAXONOMIC STUDY OF THE SALPIDAE METCALF. 



11 



series of increasingly developed eyes. The character of the rod cells 

 in the imperfect eyes of the more aberrant Salpidae seems clearly to 

 indicate degeneration. A typical rod cell from any well-developed 

 Salpa eye would be about as shown in figure 1. Compare this with 

 a group of rod cells from, say, Pegea confed 

 erata (fig. 2). In the former the glassy mod- 

 ification of the protoplasm, which constitutes 

 the "rod" (represented in black in the figures), 

 is regular and is found at one end of the cell, 

 as is characteristic of the rod cells of the eyes 

 of vertebrates, of Amphioxus, of the ascidian 

 tadpole, and of most invertebrates. On the 

 other hand, in those species of Salpidae whose 

 eyes I would consider degenerate, the rod cells 

 are very irregular in shape, are irregularly crowd- 

 ed into masses instead of being arranged as a reg- 

 ular epithelium, and each rod cell has the pro- 

 toplasm usually of its whole periphery con- 

 verted into the typical glassy substance, this fig. i.— a schematic repre- 

 glassy layer being of different thickness in dif- ll^^Zt smGLE ROD 



° J J & . CELL AND FOUR PIGMENT CELLS 



ferent rod cells and in different portions of the from the eye of a salpa. 

 same cell. FK0M METCALF (1893 ' c) - 



Taking, then, as our starting point Cyclosalpa pinnata, which, from 

 the arrangement of its muscles and -the structure of its eyes, seems 

 one of the two most primitive of the species of Salpidae, let us note 

 its general structure, giving attention to a few new 

 features we have discovered. Then let us briefly 

 review the anatomy and development of its eyes, 

 as already described by Metcalf (1893, c). Having 

 refreshed our memories of the salient features in 

 this species, we can proceed to comparisons with 

 other species. 



Cyclosalpa pinnata is represented in the collec- 

 tions of the United States National Museum by 

 the following catalogue numbers: 



Cat. No. 6460, U.S.N.M. (solitary form) from 

 Naples Zoological Station; two specimens. 



Cat. No. 6461, U.S.N.M. (aggregated form) 

 from Naples Zoological Station; nine specimens, 

 united. 



Cat. No. 6553, U.S.N.M. (aggregated form), Albatross station D, 

 5456, east coast of Luzon, San Bernardino Strait, to San Miguel Bay, 

 Philippine Islands; June 7, 1909; surface; surface temperature 86° 

 F.; one specimen. 



Fig. 2.— Pegeaconfeder- 

 ata, a group of rod 

 cells from the dorsal 

 eye of the aggregated 

 zooid. Observe their 

 irregularity of form 

 and the irregularity 

 of form and the un- 

 equal thickening of 

 theirjcell "walls. x340 

 diameters. 



