BY R. VON LENDENFELD, PH.D. 333 



It follows from this that the high development of the Mesoderm 

 of the Sponges which has doubtlessly been developed and fixed in 

 such a degree, during a very long series of generations, must 

 finally have commenced to make its appearance in the larva, 

 particularly if this was not only not disadvantageous but useful 

 for the larva. This latter is doubtlessly the case with the silicious 

 spicules which make their appearance so very early in the larva, 

 and have saved many of them from being eaten. I don't believe 

 that the free ancestors of the Sponges ever possessed a skeleton, 

 this will, according to all analogy, have been formed as a conse- 

 quence of the sessility. 



The third reason, lastly, which Balfour brings forward to prove 

 that the Sponges are not Ccelenterata, is therefore of particular 

 interest, because it is one of those which induced Leukart to 

 decide for the Ccelenterate-nature of the Sponges, only that 

 the one author puts the differences between the development 

 of the gastral cavity in Sponges and Ccelenterata forward, whilst 

 the other attaches particular importance to the similarity of the 

 two ; but we know that when we have to do with modifications of 

 homologous organs, as evidently in this case, the affinity must be 

 considered as a proof of the old genetic connection, and is 

 therefore the essential part, whilst the difference points to a special 

 attainment, and is therefore accidental. 



In both groups we see that a canal system has been differentiated 

 which extends centrifugally from the gastral cavity, which often 

 penetrates the Ectoderm (in Sponges, with the exception of the 

 problematic Physemaria always), and which opens with constant 

 or variable pores outward ; where tentacles are met with, the 

 canal can enter them and here (Actinia) or also in other places 

 (Rhizostomse), can open outward with pores ; and as in the latter 

 case astomy occurs, nourishing materials are taken up through these 

 pores just as in the Sponges. 



Ciliated cells are widely spread in the gastral cavity of Ccelen- 

 terata, if they also don't mass themselves locally to form ciliated 

 chambers. But this is also by no means the case with all Sponges. 



