REPORT ON THE KERATOSA. 77 



however, an upper group. This latter statement demands an explanation. The fact is 

 that Carter does not follow the, so to speak, " dendroid " principle of classifying Porifera 

 recommended by Gray ; he does not adopt his subdivision of Porifera into two chief 

 groups, that of Calcarea and that of SUicea,^ but subdivides the whole type or subtype 

 of Porifera into eight equivalent groups (orders), leaving the reader entirely uncertain 

 how the mutual affinities of these eight orders are to be graphically expressed, — whether 

 by eight radial branches from the same spot, or by one chief branch with secondary^ 

 tertiary, &c., ramifications. I lay great stress upon this. Our present aims are not only 

 of purely systematic, but also of phylogenetic, character, and the more the most 

 experienced spongiologist of our day, Mr. Carter, has the right to express his opinions on 

 the question, the more one must feel disappointed to find in his system an arrangement 

 which, neglecting the usual laws of the systematic, and yet not accompanied with 

 an explanatory genealogical tree, leaves the reader in the mist of uncertainty as to 

 whether its author regards, e.g., the Calcarea as forming a group systematically equivalent 

 to that, for instance, of Psammonemata, the Ceratina equivalent to the Hexactinel- 

 lida, &c., or not. Apart from these more general questions, the opinions of Mr. Carter 

 as to the affinities of horny sponges are clear ; in harmony with Gray and Bowerbank 

 he composes his third family of Psammonemata (Pseudohircinida) of groups devoid of 

 proper spicules and again of groups provided with them. The opinions of difi'erent 

 spongiologists as to the question I am now discussing are thus very contradictory and 

 even conflicting, but although most of them are expressed in very decided language, it 

 would yet be a hopeless task to search into their papers for any grounds in favour of 

 suggestions upheld by them ; these grounds are shrouded in darkness. Moreover, the 

 decided language just alluded to is often at variance with other suggestions of the same 

 author. Thus, for instance, with respect to 0. Schmidt. On page 36 of his work on the 

 sponges of Algeria he lays stress on his Ceraospongiae and Chalineae being quite natural 

 and independent families; on the following page of the same work he says that he feels 

 certain that " gewisse Gattungen einer Chalinese zu nennenden Familie unter sich weit 

 weniger als mit bestimmten Gattungen der Ceraospongise, direct verwandt sind." Under 

 such circumstances there remains no other way of elucidating the matter but to turn to 



' Dr. Vosmaer (Report on the Sponges dredged by the " Willeni Barents," p. 3), agreeing with this proceeding, but 

 not content with the designation of Silicea, since it embraces forms like true Keratosa or Myxospongije, i.e., forms devoid 

 of any siliceous spicules, proposes for it the name of " Non-calcarea." I believe this to be scarcely an amelioration. There 

 are indeed cases when negative designations are very fortunate. On the whole, however, they are not to be recom- 

 mended, and certainly not with respect to the Non-calcarea of Vosmaer. The name of, e.g., Acrania, Haeckel, being 

 negative, includes nevertheless a systematically important positive allusion. That of Non-calcarea is devoid of it. 

 I agree that it is illogical to call SUioea inter alia sponges without arjy siliceous spicules, but though illogical this 

 designation is in possession of a phylogenetic sense. As the reader will see later, there can be no doubt as to the 

 fact that Keratosa, like Myxospongias (these latter perhaps not directly, but this does not alter the case), owe their 

 origin to siliceous sponges, and from this point of view there can be no objection to the grouping of all these closely 

 allied sponges under the general name "Silicea" — as nobody finds it strange that the order of Diptera includes forms 

 like Pulex irritans or the type of Arthropoda animals like Rhizocephala or Tardiyrada. 



