118 M. E. Hiickel on the Organization of Sponges^ 



moiith-openin,2:, this apparently so wonderful proceas would 

 not, in tact, be moi*e Monderful than the ])roduction of the 

 coenohium of a Nanha or Xardojjsis from a stock of Lenco- 

 solenia^ which may at any time be traced ontogenetically. 

 Thus the lower cwnobia of the Ccenosyca appear actually 

 ■well iitted to elucidate the production of the higher cocnobia of 

 the much more perfect Echinodermata. 



Peculiar as tne Xardoj}sid(P and Coenostomidce with their 

 single cormostome may aj)pear, they (or at least the former) 

 are imited by transitive intermediate forms with the Leuco- 

 solenirr from which they have jiroceeded. Such transitive 

 forms are the Tarromida', in which the sponge-stock possesses 

 not one, but several cormostoraes, and in which, therefore, the 

 mouth-openings of the "persons" are not all fused together 

 into one, but in groups into several separate stock-mouths. 

 On the other hand, however, the advancing amalgamation of 

 the mouth-openings originally present may lead to their com- 

 plete disappearance, as in the astomatous sponges already 

 cited. Both the individual "persons" [ClistoJi/nthus) and 

 the stocks composed of several "persons" (Aidoplegma) may 

 lose their original mouth-openings by secondary fusion. Hence 

 there are among the Calcispongiis both individual forms with 

 cutaneous pores, but without a mouth {Clisfoh/nflius, Aido- 

 jjlegina), and also opposite forms Avitli a mouth but without 

 cutaneous pores {Prosgcum). 



The phenomenon here touched upon, namely, that the ap- 

 parently opposite and extreme structures are united by tne 

 interposition of a chain of gradual transition-forms, and that 

 consequently the unity of the type of organization, /. e. the 

 unitv of descent, displays itself throughout, notwithstanding 

 the greatest multifariousness in the details, strikes the critical 

 and unprejudiced naturalist everywhere among the Calci- 

 spongiffi, as, indeed, among the sponges generally ; and this 

 causes their study to appear so extremely instructive and so 

 uncommonly fruitful, especially for the understanding of the 

 descendence theory. The entire natural history of the sponges 

 is a coherent and stril-ing argument ''''for Darwiny Fritz 

 ^liiller and Oscar Schmidt have already put forward many 

 particular examples of this undeniable fact, and I have myself 

 everywhere found it perfectly confirmed. The organism of 

 the sponges has evidenth' kept itself, down to our time, so 

 fluid, so mobile, and so flexible, that we may here most plainly 

 trace step by step the origin of the different species from a 

 common stem form. 



In this respect two forms of sponges may be indicated as 

 quite peculiarly instructive and mteresting. Tliese are Mi- 



