SAlil'IDAE — FORMS WITH COVERING FOLDS. 



433 



B. Forms with Covering Folds. 



The development <>t" the forms belonging to this type (.>'. (Cyclo&alpa) 

 pinnata, S. africana-maxima, S. rundnata-t'»s/j'ornu's, S. p-nndatu) 

 differs in many essential points from that <>f S. democratica-niucronata. 

 The principal distinction consists in the presence in the former of an 

 external covering which after the degeneration of the primary brood- 

 sac (present also in S. democratica-niucronata), forms a secondary sac 

 investing the embryo, and in the peculiar development of the placenta. 

 The development of the organs also appears to follow another type.* 

 The forms just mentioned seem to agree fairly well in their develop- 

 ment, which has been studied by many zoologists, especially by 



B 



\ 



th 







.->■ ■ 





m 



u 



>**; 



Fig. 217.— Two ontogenetic stages of Salpa pinnata (after Salenskt) forming a 

 sequence to Fig. 210 B. b, blastomeres ; bk, "blood-forming bud"; hi, blood- 

 cavities in the placenta ; bl', median blood-sinus ; d, roof of the placenta (basal plate) ; 

 e, lower part of the epithelial prominence, known later as the placental membrane ; 

 e', upper part of the epithelial prominence (Salensky's ectoderm-germ) ; ./', folliculai 

 cavity ; fh, covering fold ; fvo, follicle-wall. 



Todaro, Bakkois and Salensky, and more recently by Brooks 

 (No. [.), Heider (No. XIIL), and Korotneff (Nos. XX.. XX".. 

 and XXIa.). The following account relates chiefly to S. pinnata, a 

 comparatively well-known form. 



Starting with the embryonic development of S. /linnntd at the 

 stage depicted in Fig. 217 A, we find conditions in fairly close agree- 

 ment with those described in connection with S. democrotica. The 

 embryo consists of large and of small cells. The protoplasm of the 

 large cells (b) breaks up in a peculiar way into polygonal portions 



[See footnote, p. 423 and p. 445. — Ed. 

 FF 



