210 Mr. W. S. Kent on the Relatio7iship of 



Ignoring this system, substantiated as it is by well-marked 

 structural characteristics, he proposes to substitute in its place 

 one primarily dependent on mere external resemblances, thus 

 leading us back to the same stage we had arrived at exactly 

 one century ago. 



Hackel's proposed system of redistributing the Coslenterata 

 is, in the first place, to separate it into two sections, which he 

 distinguishes as bush-animals (Thamnoda) and sea-jellies 

 Medusas). The first of these he further separates into the two 

 classes of the sponges (Spongiffi) and corals (Corallia), and the 

 second into that of the umbrella-jellies (Hydromedusa;) and 

 comb-jellies (Ctenophoree). In which of these classes the 

 Hydroid Zoophytes (comprising the Hydridae, Corynidge, and 

 Sertularidaj) are to be included, there is no indication whatever, 

 and it is scarcely to be inferred that he would incorporate them 

 with the coral-forming Actinozoa. 



Having viewed Hackel's elevation of the Spongiadee to the 

 rank of true Coelenterates, Ave next search for the evidence 

 promised in support of the very sweeping change he seeks to 

 effect. 



In the first place he states that the actual homology which he 

 presumes to exist between the sponges and corals has hitherto 

 been, for the most part, overlooked in consequence of the inves- 

 tigations of zoologists iDeing almost entirely confined to the two 

 common forms Spongilla and Euspongia, which he considers to 

 differ considerably from the original and typical structure of 

 the entire class ; and he says that the legion of the Calci- 

 spongiaB is much better calculated to shed a light upon their 

 typical organization and their true affinities. One sponge, 

 however, belonging to his chosen legion ( Grantia comp)ressa, 

 indigenous to our coasts) has formed the subject of particular 

 investigation by Dr. Bowerbank and other naturalists ; and 

 though the different regions are modified in this species to a 

 considerable extent, the same type of structure is essentially 

 predominant. The central excurrent cavity, fig. 1 Z), of 

 Spfongilla, for instance, is in Grantia developed to a marvel- 

 lous extent, and this at the expense of the complex interstitial 

 canal-system, which is almost entirely rudimentary. The 

 functions of nutrition, however, are carried out upon precisely 

 the same principle, the pabulum being received into the body- 

 mass at the pores, and, after undergoing digestion, being ex- 

 creted at the oscula, as in other Spongiadte ; and, in fact, this 

 species is the form in which the ciliary action and the cha- 

 racteristic incurrent and excurrent flow of the water before 

 described has been viewed with greater facility than in almost 

 any other. 



