208 Mr. H. J. Carter on 



the "conuli," while the space between the conuli would be 

 more or less occupied by the " apertures " or pores. Still 

 the conuli are by no means present on all sponges, and they 

 are especially absent on the slippery surfaces of the Carnosa, 

 while they are perhaps most typically developed on some of 

 the Psammonemata ; but the former is the exception. 



Again, they are of course subject to variety in composition, 

 being spiculiferous in the spiculiferous sponges, simply kera- 

 tose in the Ceratina, and areniferous in the Psammonemata. 

 Also subject to variety in form, since they may consist of a 

 simple point, and this may be single or grouped; or obtusely 

 pointed singly or en groupe ; or by extension in line and 

 uniting with one another form a reticulation which may be 

 more or less general ; but in all cases the points are origi- 

 nally covered by the dermal sarcode, that is, in their natural 

 state, although often naked and protruding afterwards. 



] t is necessary to be prepared for all these modifications, or 

 the same thing may be described indefinitely under different 

 names. 



The same may be said of the " investing " or dermal mem- 

 brane itself, which in the spiculiferous sponges may or may 

 not be charged with spicules (chiefly the minute or flesh- 

 spicules) which are more or less arranged in a reticulated 

 form, so that the pores may be in the interstices ; or it may be 

 traversed by a soft fleshy fibrous reticulation, as in the Cera- 

 tina ; or charged with foreign microscopic bodies (sand, 

 fragments of sponge-spicules, ccc), as is often the case in the 

 Psammonemata, where they may assume a similar form ; but 

 in all instances the reticulation may become so thickened as 

 to obliterate the interstices and so pass into a simple incrus- 

 tation, wherein, however, holes for the pores are always 

 preserved, because these are essential to the existence of the 

 sponge. 



As regards the mineral element, this may be produced by 

 the sponge itself or borrowed from the exterior; the former 

 is the case with the spiculiferous sponges and the latter with 

 the psammiferous ones. Of course in the spiculiferous sponges 

 the spicules, which have been termed " proper," are all of one 

 or more forms and all entire ; whereas in the borrowed 

 material, which has been termed " foreign," they are gene- 

 rally of many kinds and mostly fragmentary, more or less 

 mixed up with other microscopic objects, sucii as grains 

 of sand &c. ; but the predominance of one more than the 

 other will depend upon the prevailing element in the locality 

 where the sponge may be growing. At the same time it 

 cannot be denied that, in some instances, the sponge itself 



