EEPORT ON THE CALCAEEA. 5 



came to his later systematic ideas really in consequence of the discovery just mentioned, 

 the medal has a reverse. For, having adopted the principle of classification according 

 to the spicules, Prof. Hseckel fell into the same error which characterises the system 

 adopted in the Prodromus. The difference between a colony of Calcarea, in which, 

 according to their spicular characters, one individual belongs to one genus, the other to 

 another, and a genus such as Thecometra or Sycometra of the Prodromus, is of quan- 

 titative not qualitative nature. The existence of such colonies is indeed very instructive, 

 but it proves nothing but the great variability of the spicules, nothing but the utter 

 impossibility of giving to the presence or absence of quadriradiate or acerate spicules the 

 significance of a generic character. 



The interesting experiments of Schmankewitsch are certainly still present in the 

 memory of every zoologist. They aroused great attention, and there was considerable 

 doubt as to their reliability. But they merely amounted to a demonstration of the 

 transition of one species into another, under the influence of different conditions. Now, 

 in Ascaltis darwinii, Ascandra liebcrhihnii, and in Ascandra variabilis, we have, 

 according to Haeckel, to deal with colonial forms, which, under the same conditions, con- 

 sist partly of the representatives of one genus, partly of another. As I said before, there 

 is in the Monograph no trace of an argument to prove the naturalness of its twenty-one 

 genera. I have only to add that, had such an attempt been made, and had the argument 

 been lucid and logical, yet in view of such examples every impartial investigator would 

 look on it with distrust, and consider the argument to be sophistical. Prof. Hseckel calls 

 his system " natural," but no system paying attention to but one character and not to 

 the whole organisation can claim that designation. And so far as concerns its twenty- 

 one genera, the system proposed by Prof. Haeckel, however ingenious, is yet not less 

 artificial than that of the animal kingdom established by Linne. I do not consider it 

 necessary to dwell longer on this question, but formulate my conclusion thus : — 



The spicules of Calcarea being very variable in every direction, could not serve as a 

 basis for the distinction of genera, even if there were in the calcareous sponges no other 

 characters fit for very distinct systematic definitions. 



I pass on to the other characters. One of them — the arrangement of the canal 

 system — is used by Prof. Eheckel as a family character. 



The great difference between an Ascon, a Sycon, and a Leucon had been already recog- 

 nised in some measure by the earlier spongiologists (Bowerbank, Lieberkiihn, 0. Schmidt), 

 although the meaning of the difference was, so to speak, rather dimly felt, not appreciated 

 at its full value. It is the great merit of Prof. Hseckel that he laid stress upon these 

 differences, the more so because, as we shall see, his knowledge of the internal organisation 

 of Calcarea was far from perfect. With respect to the Ascones, I have nothing 

 further to say, Prof. Haeckel's erroneous opinion upon their histological structure, as well 



