16 Mr. H. J. Carter on the Anatomy 



Position of Surface- Spimles. 



Where a spicule which has a point projects beyond the 

 surface of the sponge to which it belongs, that point will be 

 always outermost ; but, of course, where both ends of the 

 spicule are equally obtuse or bulb-like, an obtuse end must be 

 outermost. 



Still, as sponges are wont to seize with their sarcode any 

 minute object that may impinge upon their surface, it is 

 possible that, if this be a pointed spicule with one obtuse 

 end, tlie latter may be outermost. But here the spicule does 

 not belong to the sponge, it is a foreign object ; and thus it 

 becomes very desirable to distinguish between such foreign 

 objects and the " proper spicules " of the sponge, so that the 

 former in the description of the species may not be set down 

 as part of the spicule-complement. 



Monstrosities. 



Again, spicules are much subject to monstrosity; and 

 therefore it is very desirable to find out the staple form first, 

 and describe or figure this, after which the others may be 

 figured as monstrosities. 



Development of the Fibre. 



Although the fibre appears to originate in a cell which puts 

 forth buds or processes ('Annals,' 1872, vol. x. p. 107, pi. vii. 

 fig. 5, c, d, e) in plurality, and these in juxtaposition may, by 

 elongation and anastomosis, produce a uniformly reticulate 

 structure whose simple tubular core may be continuous and 

 without foreign objects, like the " fine, uniformly granular " 

 one above mentioned, still the final enlargement of the fibre 

 by concentric layers throughout its whole course must be derived 

 from the intercellular sarcode in which it is imbedded, just as in 

 that of the spicule, whose substance being siliceo-albuminous 

 renders the process identical with the formation of the glass- 

 like fibre. 



But although the extension of the fibre and the spicule 

 respectively may be produced by a linear bud-like growth of 

 the original cell in the first instance, these cells do not appear 

 to me to be afterwards identified by their products, as Fritz 

 Miiller and others have fancied from the corneo-stellate form 

 of the fibre in Darwinella aurea = Aplysina corneostellata (see 

 'Annals,' 1872, vol. x. I. c. antea). Each structure has its 

 peculiar origin and product distinct from the other. 



So far we can understand the formation of the "simple fibre" 



