G8 



EMBRYOLOGY 



Calycophoridas. — The development of Epibulia auran- 

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

 followed by Metschnikoff (No. 18), 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 i), nc) and of the tentacle (E^ig. 30 B, t) 

 are developed. The former is developed by the invagination 

 of a solid bud-nucleus {Knospenhern), in which the cavity 



Fig. 30. — Three larval stages of EpihuUa o^lrantiaca (after MEiscHNiKOFr, from 

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

 menis of nectocalyces (iic) and tentacles {() ; C, somewhat older stage with gastral 

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

 so, fundament of the so-cuUed somatocyst; Inj, entoderm ; ep, ectodeim. 



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, hj) 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 gastrovascular cavity (Fig. 30 (7), which is 



