3o0 Mr. E. A. Minchin on the 



von Lendeni'eld's classification *, the latest in the field. The 

 obviously unnatural system of Hackel induced Polejaeff f to 

 place all the species of Ascons together in one genus, and 

 most authors, since the publication of his work on Calcarea, 

 have followed his example; but this is undoubtedly going too 

 far, and such an arrangement can only be regarded as 

 provisional. 



Having been engaged for some years now in detailed 

 investigation upon the histology, system, and development of 

 the Ascons, I have been gradually led to recognize certain 

 well-marked and, I believe, natural groups among them. As 

 I hope soon to publish an account of the development of a 

 number of species, it seemed to me best first to make an 

 attempt, perhaps somewhat rash, to fix the nomenclature of 

 at least the commoner and better known species of Ascons in 

 accordance both with their natural afiinities and with the 

 laws of priority as regards their generic and specific names. 

 A perfect classification can be obtained, of course, only when 

 all species of Ascons have been studied, and as I cannot 

 claim to have done that, my system is not to be expected to 

 be absolutely complete ; but I believe that, so far as it goes, 

 the classification I am now about to put forward is a natural 

 one, and that it indicates the lines upon which Ascons in 

 general will have to be arranged. Since, moreover, the 

 species 1 have investigated are, for the most part, just those 

 which have been longest known and earliest described, it is 

 by them that the generic nomenclature of the group as a 

 whole must be determined. I hope to make up for the short- 

 comings of the present memoir in a subsequent work, where 

 I shall treat the subject more fully and extend ray classifica- 

 tion to all known Ascons. 



Before proceeding further, however, I must first protest 

 against a notion which has been prevalent since Hackel's 

 writings, and due largely to tliera, namely that the form of 

 an Ascon colony is useless for purposes of generic or specific 

 determination. It cannot be denied that many classifications, 

 based upon external form, have been tried and found wanting ; 

 but this seems to me to be due to two causes — first, that the 

 individuals selected were often such as had not yet attained 

 their full growth and characteristic form, and, secondly, that 

 the very great changes in appearance due to contractility were 

 overlooked. Both these propositions may be illustrated from 



* " Die Spongien der Adria," Zeitschr. f. wiss. Zool. liii. (1891) 

 pp. 185-321 and pp. 361-433, Taf. viii.-xv. 



t " Report on the Calcarea," * Challenger ' Reports, Zoology, vol. viii. 

 part 2. 



