526 E. A. MINCHIN. 



or are even slightly clubbed — an uncommon form of spicule 

 ray. Whether this form of ray with persistent apical cell 

 is more primitive than the more pointed rays or not I am 

 unable to say, but it seems probable. Even in CI. clathrus, 

 however, the apical cell by no means invariably persists. In 

 the majority of cases the spicule ray simply has a single 

 fusiform cell at or near its distal extremity, as in the forms 

 described above. 



(2) The Influence of the Nucleus on the Secretion 

 of Lime. — It may be of interest to bring together the facts 

 observed which indicate a relation between the nucleus and the 

 secretion of the spicule. These are (a) the deeper stain, in 

 many cases, taken by the nuclei of the secreting cells; (b) the 

 fact that the nucleus places itself in the region of greatest 

 activity ; for instance, in the case of the rays of the triradiates 

 the nucleus of the basal cell remains near the base of the ray 

 till it is fully formed, and then moves along towards the tip, 

 superintending, as it were, the work to be done; (c) the 

 division of the nucleus where the secretion is carried on over a 

 considerable length of ray, as in the case of the long gastral 

 rays of reticulum and contorta, or the large monaxons of 

 Clathrina, sp. dub.; and (d) finally we may refer to the 

 chromatin-like bodies scattered over the spinous portion of the 

 gastral rays of cerebrum. So far as can be judged from 

 surface views, the minute sclerite always makes its appearance 

 in the immediate neighbourhood of the nucleus. 



(3) The Granules of the Dermal Layer. — We have 

 seen that all the cells of the dermal layer contain very charac- 

 teristic granules, to which in the first place the colour of the 

 sponge is due. When the sponge is any other colour than 

 white, the colouring matter is contained in the granules of the 

 dermal layer, and is rapidly dissolved out of them by alcohol. 

 The granules attain their greatest development in the poro- 

 cytes, where they were clearly described by Metschnikoff ; but 

 they are also present in the flat epithelium, and usually in 

 great abundance. They are always found in the young spicule- 

 secreting cells ; but while in the case of the triradiate systems 



