THE POSITION OF SPONGES, ETC. 433 



ectoderm disappears, and the entire sponge is built up of 

 endoderm, as he claims to have observed in the develop- 

 ment of Spongilla. On the other hand, "the coelenterate 

 nature of sponges or their close relationship with the Cni- 

 daria is not in any way supported by their developmental 

 history ". 



This theory has been further supported by Goette's 

 pupil, Noldeke (1894), who comes to the following con- 

 clusions (p. 185) : — 



"(i) Sponges possess a typical gastrula with ectoderm 

 and endoderm, which have the typical relations of position 

 to one another. 



"(2) The further development of the germ-layers of 

 sponges does not correspond with that known as typical. 

 The ectoderm undergoes a process of degeneration after 

 fixation of the larva, in consequence of which it takes no 

 share in building up the perfect animal. 



" (3) Sponges have no genetic relationship with the 

 rest of the Metazoa anywhere above the gastrula stage." 



{b) The Sponges as Coelentei-ates. 



This is to a great extent the dominant view of sponge 

 af^nities ; it is the view to be found in most text-books, 

 and generally held by those who are not themselves ex- 

 perts on the question, a fact doubtless largely due to the 

 great names that endorse this opinion. It must not be 

 supposed, however, that here, any more than among the 

 supporters of other theories, shall we find unity of opinion. 



The view that sponges were true ccelenterates was first 

 put forward definitely by Leuckart (1854, p. 472) in the 

 following words : " If we imagine a polyp colony with im- 

 perfectly separated individuals, without tentacles, stomachal 

 sac and internal septa, we have, in fact, the image of a 

 sponge with its large 'water canals' opening outwardly". 



It was, however, Haeckel who first brought this view 

 into prominence. After his pupil, Miklucho-Maclay, had 

 already (1868, pp. 236, 237) affirmed the common descent 

 of sponges and ccelenterates, Haeckel in 1870 laid down the 

 following thesis: "The sponges are most nearly allied to 



