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Prof. A. Dendy. 



in this species, but I have been able to demonstrate with the greatest ease 

 that they swell up on the addition of water just as they do in the Australian 

 sponge. 



In the Indian Ocean species they are also associated with large numbers of 

 minute palmate isochelae of the usual Clathria type. Indeed, until I 

 discovered their property of absorbing water and swelling up, I had no doubt 

 that the colloscleres in this sponge were merely modifications of these isochelae, 

 with the space between the shaft and palms filled up with silica, a view which 

 was strongly supported by the occurrence of what appear to be intermediate 

 forms. 



In Colloschroplwra arenacea I have seen only one or two isochelae and it is 

 doubtful if such spicules any longer form a normal constituent of the very 

 degenerate spiculation, though here again one occasionally sees what look like 

 intermediate forms between colloscleres and isochelae (fig. la). 



In view of the generally accepted ideas as to the intracellular origin, not 

 only of chelae, but of microscleres in general, it would no doubt be premature 

 to insist upon the homology of the colloscleres with isochelae. Such ideas, 

 however, are not based upon a very firm foundation. It seems not impossible 

 that what have hitherto been taken to be the nuclei of mother-cells are 

 really, at any rate in the case of the chelae, entire scleroblasts adhering to the 

 spicules, while the supposed membrane of the mother-cell is the wall of an 

 extracellular spicule-vesicle. Further investigations into the origin of 

 siliceous microscleres are urgently called for, and until these have been carried 

 out it is inadvisable to propound any general theory on the subject. The 

 occurrence of gelatinous spicules is in itself, however, such a remarkable and 

 unique phenomenon that it seems desirable to place it on record without 

 further delay. 



Genus Collosclerophora n. gen. 



Diagnosis. — Tetraxonid sponges with gelatinous microscleres (colloscleres). 

 The normal skeleton is almost entirely replaced by sand-grains. The 

 megascleres are slender strongyla. 



The type-species of the genus {Collosclerophora arenacea) is a typical sand- 

 sponge with much reduced spiculation, and were that species alone available 

 for study it would hardly be possible to form a definite conclusion as to its 

 proper position in the tetraxonid series. Fortunately the Indian Ocean 

 species, which will be described in my Eeport on the Sponges of the 

 " Sealark " Expedition, still preserves a full complement of both mega- and 

 microscleres, which enables me to refer it without hesitation to the 



