136 C. E. Beecher — Development of the Brachiqpoda. 



Terebratulina has a tuft of bristles on the top of the 

 cephalic segment, In Lacazella, the bundles of setse are 

 absent, and the head is more distinctly differentiated from the 

 anterior segment than in Cistella. The closing cephalula stage 

 in Cistella has an umbrella-like expansion of the cephalic bor- 

 der, and the organism becomes a free swimming larva, figures 

 7-9. 



Cistella neapolitana Scacchi. 



Figure 5. — Neoembryo. Embryo of two segments. 



Figure 6. — Neoembryo. Cephalula, ventral side; showing cephalic, thoracic, 



aDd caudal segments, eye spots, and bundles of setae. (5, 6, after 



Kovalevski.) 

 Figure 7. — Neoembryo. Lateral view of completed cephalula stage ; showing 



extent of dorsal (d) and ventral (t>) mantle lobes, and umbrella-like cephalic 



segment. 

 Figure 8.— Neoembryo. Same stage ; ventral view. (7, 8, after Shipley.) 



Larval stages. 



The TyjJemljryo is the larval stage at which some distinctive 

 features make their appearance, but before the special characters 

 of the class are to be found, figure 10. It is analogous to the 

 molluscan embryo in which a shell gland and plate-like initial 

 shell are developed. There is, however, no homology of parts 

 or organs between the typembryonic mollusk and brachiopod. 



In Cistella and Terebratulina the development of the typ- 

 embryo has been observed, and consists of the folding 

 upwards of the lobes which have been developed from the 

 thoracic segment to form the mantle, so that they gradually 

 enclose the anterior end, figures 24-27. The surfaces of the 

 mantle which were exterior in the cephalula have now become 

 inner and the bundles of setse have revolved 180°, changing 

 their direction from posterior to anterior. This leaves the 

 lower part of the thoracic and the whole of the caudal seg- 

 ment exposed. The outer surface of the mantle is invested 

 with a hard integument, which, upon completion, and before 

 the growth of the true shell forms the protegnlum. The 



