1 M. E. Hiickel on the Or<janizatton of Sponges, 



sponge-hodi/ seem to constitute a more substantial objection to 

 our interpretation. It is well known that generally (but not 

 always !) the direction of the flow of the water which passes 

 through the canal-system of the living sj)onge-body is as fol- 

 lows : — The water Hows in tlirougli very numerous and tine 

 cuticular pores (the so-caUed " incurrent apertures "), usually 

 perceptible only by means of the microscope, and through 

 these tine " incurrent canals," which often ramify and anasto- 

 mose repeatedly, reaches a few larger canals, which finally 

 open into the central " excurrent cavity " (our " stomachal 

 cavity "). From this the used water then escapes outwards 

 with the useless solid particles through the " excurrent orifice" 

 (our "mouth"). 



In the corals or Anthozoa, on the other hand, as also in the 

 other Cnida?, tlie direction of the flow of the water which tra- 

 verses the cavities of the body appears to be different, and in 

 a certain sense opposed to the ordinary direction of the cuiTcnt 

 in the sponges. The water, which at the same time conveys 

 the food into the body, is usually, in the Cnidje and, especially, 

 in the corals, taken up by the mouth, passes through this into 

 the stomach, and hence into the other canals which traverse 

 the body. The part played in this process by the cutaneous 

 pores of the corals is unfortunately still as good as unknown. 

 These fine apertures in the skin, usually perceptible only 

 through the microscope, through which the finest canals of the 

 coelenteric vascular system open outwards in theeorals, just as 

 in the sponges, have by no means attracted so much attention 

 in the former as in the latter. Nay, they have scarcely even 

 been compared ! Whilst the greatest importance has been 

 attached to the cutaneous pores of the sponges, those of the 

 corals, although long known, have been almost universally ig- 

 nored ; and yet the two are evidently homologous, and of one 

 and the same origin ! Nay, it is even very possible (not to 

 say probable) that through the skin of the corals, as through 

 that of the sponges, respiratory cun-ents of water constantly 

 penetrate into the body by means of the cutaneous pores, and 

 that these traverse the canals of the body-wall, and finally 

 discharge themselves into the stomachal cavity. The cuta- 

 neous pores in tlie corals might then, just as much as in the 

 sponges, be designated " incuiTcnt apertures." 



So much, at any rate, is certain, that an essential morpho- 

 logical diflerence does not exist between the nutrient vascular 

 system of the sponges and corals. If we compare single, so- 

 litary, perfectly developed persons of the two classes, e. g. 

 Sycum and Actinia, we find in both a central cavity as the true 

 princi])al part of the nutrient canal-system — a central cavity 



