434 SCIENCE PROGRESS. 



the corals of all organisms. Certain sponges differ from 

 certain corals only by a less degree of histological differen- 

 tiation, and especially by the want of urticating organs. 

 The most essential peculiarity of the organisation of 

 sponges is their nutritive canal system, which is both 

 homologous with, and analogous to, the so-called ccelenteric 

 vascular system, or gastro-vascular apparatus of the Coelen- 

 terata. In the sponges, just as in the corals, and indeed in 

 the Coelenterata generally, all the different parts of the 

 body originate by differentiation from two primitive simple 

 formative membranes or grerm lamellae, the entoderm and 

 the ectoderm. These two lamellee originate by differentia- 

 tion from the originally homogeneous cells which (having 

 been produced by the segmentation of the ovum) compose 

 the spherical body of the ciliated embryo, or of the primi- 

 tive larva (Planula). From the inner or vegetative germ- 

 lamella, the entoderm, originate the nutritive epithelium of 

 the canal system and the reproductive organs. From the 

 outer or animal germ-lamella, the ectoderm, all the other 

 parts originate" (p. 6). According to Haeckel the absence 

 of nematocysts or urticating organs in sponges and their 

 constant presence in corals, Hydromedusse, and Ctenophora, 

 is the sole morphological character separating the first class 

 from the last three (p. 7). The mark of a sponge in- 

 dividual is the osculum (p. 8), representing the Coelenterate 

 mouth. The inhalant pores of sponges find their homo- 

 logue in the cutaneous pores of corals. " Sponges and 

 corals," he concludes (p. 13), ''are near blood relations.'* 

 From the common ancestor of both, the Protascus, origi- 

 nated as two branchlets the Prosycum, ancestor of sponges, 

 and the Procorallum, ancestor of corals. 



These statements of Haeckel's were the cause of a con- 

 troversy between Kent and Lankester, the former maintain- 

 ing the Protozoan affinities of sponges, the latter defending 

 Haeckel. "Admitting," says Kent {1870, p. 204), "that . . . 

 there in all probability did exist a something equivalent to 

 Haeckel's hypothetical Pro^asais, and from which the existing 

 stock of sponges and corals has probably been evolved . . . 

 the evidence he brings forward in support of the proposed 



