08 



EMBRYOLOGY 



Calycophoridae. — The development of Epibulia auran- 

 tiaca (family of the Diphyidae), which has been very accurately 

 followed by Mrtschnikoff (No. 1H), will be described as the 

 type. The ovate planula larva exhibits a thickening of the 

 ectoderm at the posterior pole and on one side (the subse- 

 quent ventral side). Here the fundaments of the first 

 nectocalyx (Fig. 30 J5, nc) and of the tentacle (Fig. 30 B, t) 

 are developed. The former is developed by the invagination 

 of a solid bud-nuclens (Knospenkern), in which the cavity 



Fig. 30.— Three larval stages of Epihulia ourantiaca (after Metschnikoff, from 

 Balfour's Comiiarative Emhryology). A, planula; B, stage six days old with funda- 

 mems of nectocalyces (nc) and tentacles (t); C, somewhat older stage with gastral 

 cavity ; nc, nectocalyces ; t, fundament of tentacle ; po, polypite ; c, nutritive cells ; 

 to, fundament of the so-called eomatocyst ; hy, entoderm ; ep, ecioderm. 



of the bell is soon formed ; the fundament of the tentacle 

 at first consists of a simple invagination of the body-wall, 

 in which two layers take part, the development of an 

 ectodermic layer (Fig. 30 B, hi/) along the ventral side, con- 

 sisting of small cells, having already taken place at this 

 stage. The next important change consists in the establish- 

 ment of the gastrovascnlar cavity (Fig. 30 0), which is 



