the Sponges to the Corals. 209 



The shallowness of Lcuckart's hj-potlicsis, in a measure 

 supported by Iliickel, of a polyp-colony with imperfectly 

 separated individuals, devoid of tentacles, stomachal sac (ali- 

 mentary canal), and internal septa, being the image of a 

 sponge with its large " water-canals " (oscula) opening in- 

 wardly, here becomes most evident. Such an organism could 

 not exist ; for a polyp or polyp-colony bereft of its tentacles, 

 and as a matter of course of its prehensile lips, though it might 

 be hacked into somewhat the outward resemblance of a 

 sponge, would be entirely deprived of its means of subsistence, 

 and would, sooner or later, inevitably perish. 



The few facts already adduced suffice to show that the two 

 organisms arc most distinctly and widely separated from each 

 other. There arc numerous other points, Iiowevcr, which can 

 be best indicated in following up Hackel's line of reasoning, 

 that demonstrate still further that the sponges cannot be con- 

 sistently incoi"]3orated with the Coelenterata. In the first 

 place, Iliickel endeavours to show that the peculiar canal- 

 system of the sponges is not a perfectly specific nutritive ap- 

 paratus, such as occurs in no other class of animals, notwith- 

 standing that he at the same time admits that all recent 

 zoologists who have gained most credit for their systematic 

 investigations of the class consider it to be so. 



In opposition to tliis generally received opinion, he starts 

 with the proposition that " The sponges are most nearly 

 allied to 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 tlie organization of the sponges 

 is their nuti'itive canal-system, which is homologous with and 

 analogous to the so-called gastrovascular apparatus of the 

 Coelenterata." 



This latter portion of his proposition is certainly somewhat 

 startling, after considei-ation of the facts which have been al- 

 ready stated. Before proceeding to bring forward his evi- 

 dence in support of his rather astounding proposition, he next 

 proceeds, somewhat prematiu-ely, to prepare for them a snug 

 place where they may be interpolated among, and as represen- 

 tatives of, the true Coelenterata. 



Such an end he achieves by entirely upsetting the clear 

 limits by which this subkingdom is marked out and subdivided, 

 with the nmtual consent of the most eminent naturalists of the 

 day. There is scarcely any otlier subkingdom wliich is more 

 clearly defined, under its present limitations, than the Coelen- 

 terata, or one that is further subdivided into two more clear and 

 distinct sections than that of the Actinozoa and Hydrozoa. 



