100 AßT. 1. 1. IJIMA : HEXACTINELLIDA, III. 



stage of its formation either widely communicates with that of 

 the mother or is apparently separate from, and independent of, 

 tliis. The latter condition how^ever passes ultimately into the 

 foi'mer evidently by the widening of a connecting excurrent canal, 

 as assumably the new gastral cavity itself likewise arose by the 

 widening of an excurrent canal of the mother. 



In some young specimens I have found, apart from the 

 terminally situated osculum, a roundish gap in the wall, this 

 being in no degree specially elevated at the spot. The gap is 

 sometimes surrounded by a thin iris-like membrane. I consider 

 this to be a secondarily formed osculum, formed either pre- 

 cociously at a place where an evagination of the wall may yet 

 take place or as standing alone by itself for a person in suppression 

 of the evaginating process. In the latter case, it would be exactly 

 comparable to the openings which I have called parietal or 

 secondary oscula in the Euplectellidœ. 



The originally simple stalk may possibly send out off-shoots 

 and thus change into the ramified condition seem in old speci- 

 mens ; but there are also other w^ays by which this may l)e 

 brought about. Some of the little specimens above-mentioned are 

 in contact with, and fixed to, the substratum at more than one 

 point ; in other cases, individuals of apparently separate origin 

 but growing side by side are fused together in the upper part. 

 In both cases the result is much the same, and it is easy to imagine 

 that with the growth of the sponge there should arise as many 

 stalks as there are points of attachment to the substratum with 

 variations in their arrangement according to circumstances. 



The even but gently undulating, external surface of the 

 sponge-body is covered with the extremely fine and approximately 

 quadrate-meshed dermal latticework (PL VIII., fig. 20), in which 



