48 Mr. W.J. Sollas on a new 



in these sponges. O. Schmidt says that none is present in 

 the two species he had examined ; and to determine whether 

 there might not be some in mine I mounted a few slices of 

 the sponge in glycerine jelly, which makes the siliceous 

 spicules almost invisible, and so brings into greater distinct- 

 ness the other parts. The sarcode was thus rendered very 

 visible ; but no kerataceous material could be detected. The 

 sarcode, we may mention, soon parted with some of its intense 

 yellow colouring-matter to the surrounding medium, which thus 

 at first assumed a yellow tint that has since almost entirely 

 disappeared. By the absence of horny matter in it Plocamia 

 does not quite meet the requirements of Carter's definition of 

 his order ; but this is a small point of difference ; and from the 

 examination of a large number of Echinonematous sponges I 

 am inclined to think that the presence or absence of horny 

 matter is not of ordinal value, or, more properly, that the 

 passage from a spiculose horny fibre, whether echinated or 

 not, to a wholly spicular not horny fibre is so gradual that it 

 is impossible to draw a hard-and-fast line between the two, 

 and that, just as a Renierid may be regarded as a Holorha- 

 phidote development of a Chalinid, so there may be sponges 

 among the Echinonemata which may be regarded as Holo- 

 rhaphidote developments of the Ectyonidee ; and such I believe 

 is the nature of Plocamia for one, not to mention others. 



If we adopt a monophyletic origin for the various forms of 

 spicules found in Plocamia and other sponges, we shall natu- 

 rally be led to look for some evidence of this amidst the wide 

 variations which the spicular forms assume ; and such evidence 

 is, I think, to be readily found. In the first place, leaving 

 out of account the flesh-spicules, of which we know too little 

 at present, and which may have a separate origin to the others, 

 one observes a close family likeness in all the forms of 

 spicules to be found in Plocamia : thus, though they differ 

 considerably in proportion, they all present a conical or cylin- 

 drical form, without any tendency to become fusiform, they 

 all exhibit a tendency to acquire spines, and they all vary in 

 the same kind of way. The dermal spicules, for instance, 

 often acquire an inflated head, and, though usually very 

 straight, sometimes become slightly curved ; on the other 

 hand, the large intermediate acuates sometimes lose their 

 terminal inflation and so present merely a rounded-off end, 

 and, though usually curved, they sometimes become straight ; 

 while in both dermal and intermediate acuates the head often 

 becomes more or less spined. The only constant difference 

 which distinguishes these two forms thus lies only in size and 

 proportion ; and even in the latter character variation occurs, 



