4 Proceedings of the Royal Society of Victoria. 



from wliicli the.sc six tubes originated was the terminal node 

 of a branch, and probably had not as yet reached its full 

 development, it is impossible to say how many of the six 

 young tubes would have developed into perfect branches. 

 Each one of them was short and had a rounded apex. 



It is especially worthy of note that the tubular internodes 

 are not continuous through the substance of the sandy 

 nodes, but each one breaks up on entering the sand}" mass 

 into a kind of rete mirabile, formed chiefly of the delicate 

 tubular zocecia. 



In Cryptozooih tullsoni, the type of the genus, the 

 chitinous internodes are comparatively long, and the sandy 

 nodes are well sepaiated from one another. In C. concretuon, 

 however, the internodes are very much shortened, and the 

 sandy nodes are brought close together, and in the older 

 parts may even be confluent, forming a continuous sandy 

 mass (cf iFigs. 2, 3 and 4). 



The zocEcia are very delicate and adhere firmly to the 

 sand grains, so that it is impossible to separate them. 

 Perhaps in Gvyptozooii, as in those horny sponges which 

 take on an arenaceous habit, the chitinous portion of the 

 skeleton is actually reduced in consequence of the addition 

 of the sand, which may be considered as supplementing, 

 and possibly, to a certain extent, replacing the chitiu. 



However this may be, it is very difticult to obtain an idea 

 of the true sliape and arrangement of the zooecia. I can 

 t)nly say that they are tubular, and appear to spring one 

 from another in an irregular manner (Fig. 11). The mouth 

 of the zocecium, as in all the Ctenostomata, remains soft 

 and unchitinised, and, when the polypide is retracted, is 

 pulled into the hinder part by a special series of muscular 

 bands (Fig. 11, rti.) 



The points where the zooecia arise from one another are 

 marked by oval scar-like areas — the rosette plates (Fig. 11, 

 r.'p) 



The structure of the internodes of the coenoecium wvcxy 

 best be studied in Cryptozoo)i wihoni. In that species they 

 are short, somewhat dumb-bell-shaped tubes (Fig. 5 Inn.), 

 with swollen extremities, breaking up suddenly on reaching 

 the sandy node at either end into small, irregular branches, 

 or giving rise directly to the zooecia (Fig. 5). The wall of 

 each internode appears in optical longitudinal section (Fig. 

 10), to be clothed internally with a deeply staining 

 epithelium {cp.) I have not succeeded in demonstrating 



