L-ORGANISATION AND CLASSIFICATION OF THE KERATOSA. 



One might perhaps feel inclined to say that this title promises but very little ; that a 

 classifier has to search for systematic characters not only into the organisation of the 

 animals in question, viz., into their Anatomy and Histology, but also into other regions 

 of Biology, and, in the first instance, into Embryology and Palaeontology. Unluckily 

 this is impossible so far as the horny sponges are concerned. Some fossils have been 

 described which may possibly be referred to the Keratosa, but this cannot be regarded 

 as scientifically proved, nor is the number of such forms sufficieut to permit any further 

 conclusions.^ The possibility of a future application of Palaeontology to phylogenetic 

 purposes respecting the Keratose Sponges is not entirely excluded, though there are 

 reasons to believe that this group is a very recent one, but up to the present time the 

 application above mentioned is impossible. Again, with respect to embryological data 

 even such a modest hope cannot be assumed. Of course our knowledge is stUl very 

 fragmentary, but what we know only confirms the opinion that the ontogeny of the 

 horny sponges is very monotonous, and that therefore its further profound study would 

 probably be of consequence only for the solution of certain embryological problems (in 

 the strict sense of the word), but not of much service in augmenting the number of 

 systematically important characters. The classifier is thus thrown on the resources of 

 Anatomy and Histology alone ; chiefly on those of Anatomy, since it is only in exceptional 

 cases, as in lanthella or Cacospongia vesicidifera,^ that histological characters can be 

 applied to systematic purposes. But, nevertheless, this would be of no further consequence 

 were the anatomical characters of, so to speak, unconditional value. Yet even this is not 

 the case, and this is just what renders the classification of the Keratosa so very difiicult, 

 and makes the danger of " describing individuals instead of genera and species " (0. 

 Schmidt) greater in this group than elsewhere. For Comparative Anatomy can only state 

 this or that difi"ereuce in organisation, but is very often quite powerless, at least in the 

 Keratosa, to decide the question whether this or that anatomical peculiarity is constant or 

 merely accidental. It is therefore obvious that the systems of the Keratosa we are now 

 so diligently elaborating will prove, with the progress of the Comparative Physiology, to 



1 Zittel, Zur Stammesgeschichte der Spougien, Mimchen, 1878, p. 9. - Page 58 of this Report. 



