254 



STUDIES IN EVOLUTION 



lobation of the cephalic collar in Sabella. Four figures are 

 introduced illustrating the principal changes in Spirorbis. 

 They may be compared with the development of Cisiella 

 shown in figures 90-94. 



It is not intended by this to indicate a close relationship 

 with the chaetopods, for the writer is inclined to accept the 

 opinion of Joubin,^^ that the brachiopods constitute a distinct 

 and independent class. 



The Phylembryo (figure 99) differs from the typembryo in 

 (a) the completion of the embryonic shell, or protegulum; 

 (6) the first appearance of the tentacular lobes of the lopho- 



99 



100 



Oistella neapolitana Scacchi. 



Figure 99. — Ph_vlerabryo ; brachiopod; showing shell (protegulum), begin- 

 ning of tentacles of lophophore (/), obsolescence of eye-spots, and formation of 

 oesophagus ; t, hiuge-teeth ; vp, ventral pedicle muscles. 



Figure 100. — Nepionic brachiopod ; showing distinct tentacles of lophophore, 

 mouth, and stomach, and transformation of muscles from typembryo (figure 94). 

 ad, adductors; di, divaricators; vp, ventral pedicle muscles. (Figures 99 and 

 100, after Kovalevski.) 



phore, or arms ; (c) the usual dehiscence of the four bundles 

 of setse ; (oT) the obsolescence of the eyes ; (e) the definition 

 of the cesophagus and stomach, and (/) the agreement of 

 the muscular system with that in adult forms. These fea- 

 tures, with the pedicle which appeared in a preceding stage, 

 represent the brachiopod phylum, and are properly referred 

 to the phylembryonic period of Jackson. Although the 

 molluscan stage called the prodissoconch in pelecypods, the 



