J18 XYCANDRA. 



constant for the different larvae. On the central gastrula cavity of 

 the sponge becoming placed in communication with the external 

 water, the hypoblast cells lining it become ciliated afresh (fig. G7 B, en.} 

 and develop the peculiar collar characteristic of the hypoblast cells 

 of the Spongida (vide fig. 64, hy.). When this stage of development 

 is reached we have a fully-formed sponge of the type made known 

 by Haeckel as Olynthus. 



FIG. 67. THE YOUNG OF SYCANDHA RAPHANCS SHORTLY AFTER THE DEVELOPMENT OF 

 THE SPICULA. (Copied from Schulze.) 



A. View from the side. 



B. View from the free extremity. 



os. osculum ; ec. epiblast ; en. hypoblast composed of ciliated cells. The terminal 

 osculum and lateral pores are represented as oval white spaces. 



When young examples of Sycandra come in contact shortly after 

 their attachment they appear to fuse together temporarily or else per- 

 manently. In the latter case colonies are produced by their fusion. 



Amongst other calcareous sponges the larva of Ascandra contorta 

 (Haeckel No. 126, Barrois No. 122) presents the typical amphiblastula stage, 

 and so probably does that of Ascandra Lieberkuknii (Keller No. 128). In 

 Leucandra aspera (Keller No. 128, Metschnikoff No. 134) the larva passes 

 through an amphiblastula stage, but the characters of the cells of the two 

 halves of the larva do not differ to nearly the same extent as in Sycandra. 



Although the majority of calcareous sponges appear to agree in their 

 mode of development with Sycandra, nevertheless the concordant researches 

 of O. Schmidt (No. 138) and Metschnikoff (No. 134) have shewn that this 

 is not true for the genus Ascetta (As. primordialis, clathrus and bianco). 



