IN SPONGILLA FLUV1ATILI9. 



55 



the last which has what may be truly called spicules " incipiently 

 spinous ;" for this character can only be discovered by the use of 

 a £th objective. 



Upon this, Dr. Bowerbank observes " How this British Spongilla 

 can be a variety of a species that does not exist in England, or to 

 the best of my knowledge nearer than Bombay, is quite past my 

 comprehension ; and I have, therefore, described it as a distinct 

 species, under the title of S. Parjitti" 



Before we consider the value of these differences, let me direct 

 your attention to specimens found in the Thames, all of which differ 

 from the described type, and some in their minute structure seem to 

 be identical with that found in the river Exe. Neither Dr. Bower- 

 bank nor Mr. Carter can have been acquainted witli the Spongilla 

 of the Thames, or they could not have avoided noticing the interest- 

 ing variations from the established type. Indeed, almost all the 

 characters set down are found to vary. First, as to the dermal 

 membrane, which is pronounced to be without spicules, I can show 

 you a specimen in which this organ is completely covered with 

 spicules, matted together. Then, as regards those of the skeleton, 

 examples are met with in which a portion of them take the " in- 

 cipiently spinous " condition of that found in the Exe, and others 

 pass from that into a greater development, so that more than one 

 half of the spicules of the skeleton are spinous, and the spines well 

 pronounced, until we reach the climax in which all are spined, with 

 only here and there a representative of the smooth type-form. 

 Passing from the Thames, out of which, as yet, I have not obtained 

 a single specimen of the so-called type, I shall show you an 

 example in which, though the spicules are smooth, yet both dermal 

 and interstitial membranes are thickly provided with them of a 

 slender, delicate and special character. 



It will then be a question to ask whether, following precedent, we 

 are to establish three or more species ; or, whether it is not more 

 in the interest of science to take a different course, and to endeavour 

 to embrace, under the general title of Spongilla Jluviatilis, all those 

 which possess characteristics typical of the species ; and especially 

 in the birotulate forms of the spicules of the ovaria, noting, if you 

 please, the varieties by either an additional name, or what would 

 equally satisfy, in my opinion, all that is required, an addition of A, 

 B, or C, &c. Surely it must be rather misleading than otherwise 

 to have such a title as " Spongilla Meyeni, var. Parjitti ," or even 



