of the Sponges to the Choanoflagellata. 373 



In point of fact, this idea has recently found a very decided 

 supporter in Biitschli. " As I am of opinion," says Biitschli 

 in his remarks upon the Gastrsea-theory*, " that the group 

 of the Sponges is completely shut off from the rest of the 

 Metazoa, and one which originated quite independently from 

 the section of the Choanoflagellata (Saville Kent), it appears 

 to me a mistake to take this group into consideration in the 

 elucidation of the phylogenesis of the other Metazoa." 



No doubt this opinion of Biitschli's is founded upon the same 

 fact which has induced James-Clark, Carter, and Saville Kent 

 to refer the Sponges to the Choanoflagellata, namely, the 

 striking similarity of the latter to the collared cells of the 

 Sponges. It seems natural to refer the exclusive occurrence 

 of so peculiar a structure as the collar in two groups of 

 animals, not to a possible double independent formation of it, 

 but simply to inheritance ; and as we have no reason to sup- 

 pose that the existing Choanoflagellata are retrograde descen- 

 dants of sponge-like Metazoa, but are a priori inclined to 

 assume that our lowest Metazoa originated from Protozoan 

 colonies, we are certainly easily driven to the notion that the 

 Sponges have been developed from colonies of Choanoflagel- 

 lata, of the possibility of the existence of which their unaltered 

 descendants, still existing as Protozoa, furnish the clearest 

 proof. 



With such a notion, however, the assumption of a near 

 relationship between Sponges and Cnidaria is irreconcilable. 

 We should then have likewise to derive the latter from 

 Choanoflagellata, for which there is not the least reason. 



As is well known, it was Leuckart who first, in the year 

 1854 t, on the ground of the then known facts, indicated the 

 relationship of the Sponges to the " Polypes/' and in conse- 

 quence referred them to his type Coelenterata. Although 

 this view at first met with little acceptance, Leuckart repeated 

 it in the year 1 866 J, and instituted a comparison between a 

 Orantia (Ascone) and a Hydroid polype. He indicated that 

 the simple vibratile cavity occurs in both, but that the ter- 

 minal apertures of the tubes of Grantia represent the buccal 

 apertures of the individual polypes ; while the absence of 

 tentacles, which are also occasionally deficient in Siphono- 

 phora and Ctenophora, can no more stand in the way of the 

 comparison than the occurrence of the lateral incurrent 

 orifices, which likewise occur in many Coelenterata as 

 so-called water-apertures ; and he concluded his comparison 



* Morphologisches Jahrbuch, Bd. ix. p. 424. 

 t Arch, flir Naturg. Jahrg. 20, Bd. ii. p. 471. 

 X Arch, f'iir Naturg. Jahrg. 32, Bd. ii. 



Ann. Jj Mag. 2V. Hist. Ser. 5. Vol. xv. 26 



