22 THE VOYAGE OF H.M.S. CHALLENGER. 



The Sponges also arc not to be placed among the Ccelenterata as a class, as suggested 

 by Ganin. 1 The peculiarities of their canal system, the early development of the 

 mesoderm, the circumstance that it is just the mesoderm which in them gives origin 

 to the generative products, and finally, the absence of cnidoblasta and nervous 

 elements, these latter having been recently observed in the Hydroida also (Jickeli) 2 ; all 

 these differences taken together, though perhaps not justifying the establishment of a new 

 type, are yet important enough to entitle the Sponges to occupy an independent sub- 

 division of the Ccelenterata in the position of a sub-type. That within this sub-type, 

 the Calcarea, constituting a quite isolated group, are to be opposed as an independent 

 Class to all other Sponges is so evident that I hope no further arguments in favour of the 

 position will be deemed necessary, and this Class I propose, in accordance with my fore- 

 going statements, to divide into two Orders : — 



Homoccela, including the single Family of Asconidoe (Ascones), and 



Heteroccela, including the Families of Syconidse (Sycones), Leuconidaa (Leucones), 

 and Teichonidaa (Teichonia, Teichonellidae). 



The necessity for the establishment of this third Family, the Teichonidse, having been 

 urged some years ago by Mr. Carter, 3 who described two calcareous sponges which differ 

 from all the Calcarea hitherto known, by one peculiarity of such vital importance that the 

 establishment of a new Family was really the only issue. This peculiarity consists in the 

 differentiation of the outer surface of the sponge into two quite different parts, — that bearing 

 oscula and that bearing pores, — and I am the more disposed to agree with Mr. Carter, as I 

 found amongst the Challenger Calcarea some specimens which are constant to the main 

 character differentiating the genus Teichonella, C, from other Calcarea, although they differ 

 from it in their general shape — which in a form so highly organised is not without signifi- 

 cance — and in their spiculation so much that I really cannot place them as a third species 

 in that genus, but must create a new one for their reception. 



I have now done with Orders and Families ; I return to the genera. It was 

 stated that the properties of the constituent parts of the skeleton as to whether they be 

 composed of triradiate, quadriradiate, or acerate spicules are by no means to be utilised as 

 generic characters ; and hence that the seven genera established by Prof. Hseckel in 

 each of his three Families are not natural, but artificial. 



How then is a natural classification to be devised ? The answer is easy : — by the 

 consideration of all the organs of the animal in their mutual correlation. Hseckel has 

 pointed out the high systematic significance of the canal system, and he clearly 

 understood, moreover, that the disposition of the spicules depends upon its modifications, 

 and that the disposition of the spicules in its own turn influences their form. 

 He dedicates to these questions a considerable number of pages (loc. tit., Ed. i. pp. 



1 Contributions to the Anatomy and Embryology of the Sponges, Warsaw, 1879, p. S3 (Russ.). 



'-' Morphol. Jahrk, Ed. viii. p. 373 ; Ibid,., p. 5S0, 1S82. 3 Ann. and Mag. Nat. Hist, ser. 5, vol. ii. p. 35, 1878. 



