the Spongps to the Corals. 213 



the Ma'lreporaria impcrforata, includes genera, Biich as Caryo- 

 ])h}fUia^ Fldlxlbuii, Lojihohclia, Knph)jllia, Vhijlhinijia^ and 

 numbers ot" others, in which the whole ])udy-wall is strenf^thened 

 by a coinjiact and imperforate theea, which, again, is frequently 

 rendered still more dense by the superposition of an equally 

 compact and imperforate cpithcca. A current of water passing 

 through the body-wall into the somatic cavity of these animals 

 would thus be a matter of perfect impossibility ; and even if 

 such did constantly exist, the perforations for its admission 

 would be something essentially different from the apertures 

 occupying the same position in the sponge : in the latter they 

 have been proved to be the channels through which the body- 

 mass derives all matters of nutrition, while in the Actinozoa 

 they could, at the outside, be subsei'vient only to the func- 

 tion of respiration ; the aperture subservient to nutrition, as 

 already shown, being the terminal buccal orifice or mouth. 

 The very few isolated examples of the Actinozoa, however, 

 in which these cutaneous pores have been found to exist, de- 

 monstrate beyond doubt that they cannot be subservient to so 

 important and essential a function as that of respiration. 



The next argument brought forward by Hiiekel appears, at 

 first sight, to be more formidable, though on closer inspection 

 its seeming importance vanishes. In the first place he testi- 

 fies to having examined sponges whose oscula have permitted 

 the inflow as well as the outflow of water. This condition 

 of affairs, however, appears to have been quite arr abnormal 

 one ; he cites no single instance in which the inflow of water 

 at the osculum proved constant ; and, as I shall hereafter show, 

 this temporary and abnormal condition observed by him can 

 readily be accounted for. The second and, seemingly, the 

 more important part of his argument is his statement that 

 certain sponges exist which possess no cutaneous pores at all. 

 (The advantage his theory derives from this fact, after his 

 assumption that all Actinozoa do possess them, is not clearly 

 perceptible.) On inquiry into what sponges these are, how- 

 ever, we find that they consist of only two microscopically 

 small forms, for one of which he proposes tlie name of 

 Prosycum. Now the very fact of their microscopic minute- 

 ness entirely neutralizes the force of his argument, the small 

 number of ama'boid particles which must constitute so minute 

 a sponge-mass being necessarily brought into relationship with 

 the suiTOunding element without the requirement of a complex 

 canal-system ; and for the same reason, again, they find suffi- 

 cient nutriment in the water around them (as with the ordi- 

 nary fixed Rhizopoda, to which these low sponge-forms seem 

 most closely to approximate) without being dependent on the 

 action of ciliary currents. 



