HTDROZOA. 57 



least, is the life history of the Sertularidce. The 

 young Camipamdaria or Antennularia, at first 

 free, soon loses its cilia, fixes itself, and contracts 

 into a circular disc, which exhibits a division into 

 four lobes (fig. lo, c and d). In the centre of 

 the disc an opaque spot makes its appearance, and 

 over this the surface becomes gradually elevated, 

 until, finally, a young coenosarc is the result {fig. 

 10, e). From this, by gemmation, the branching 

 hydrosoma of the complete organism, with its 

 crowded assemblage of polypites, is subsequently 

 produced. 



Thus the young condition of a Sertularid would 

 appear to differ from that of a Corynid in having 

 a portion of its coenosarc more or less completely 

 developed before distinct traces of a polypite can 

 be observed. Such a conclusion accords well with 

 the composite structure always assumed by the 

 adult hydrosoma. And in this respect the Sertu- 

 laHdcE, while departing from the Gorynidce, seem 

 to agree with the oceanic orders, Calycophoridce 

 and Physophoridce. 



Galycophorid^. Of the earher embryonic 

 changes in the CalycopJioridce little is known. 

 In DiphyeSf according to Gegenbaur, the blasto- 

 derm at first appears as an elevated protuberance, 

 occupying only a portion of the segmented vitellus. 

 Soon, this blastoderm forms a rudimentary necto- 

 calyx, from which a short canal leads to the ciliated 

 cavity of the yolk below. The nectocalyx then 

 rapidly enlarges, while polypites are seen to arise 

 between it and the appended yolk-mass. 



PhysophoriDjE. Our knowledge of the em^ 

 hijologj of the Physophoridce is confessedly scanty. 



