246 Prof. E. Hackel on the Position of the 



anatomy* ; but it is evident from tlie naive reply of the latter 

 that this well-meant endeavour was in vain f. 



The objections which Ehlers| has made against my theory 

 I cannot refute, because his conception of the sponge-organism 

 is completely different from mine. I cannot by any means 

 conceive a sponge without any internal cavity and without 

 two essentially different cell-formations (the flagellate cells of 

 the entoderm and the non-ciliated cells of the exoderm). 

 Ehlers, on the contrary, assumes two different primary groups 

 of sponges, namely '' Sjwngice holosarcincB^ with a dense tissue 

 without a canal-system, and SpongicB ccetosarcina', which de- 

 velop body-cavities " (?. c. p. 555) §. He derives the latter 

 from the former, and thinks that the Protospongice conceived 

 by 0. Schmidt as the hypothetical stock group of all Sponges 

 were " holosarciue sponges, with a simple, not differentiated 

 tissue." Unfortunately we can by no means understand from 

 Ehlers's memoir what he really regards as the characteristic 

 " tissue " of the sponges. The word " cell " occurs nowhere 

 in the whole memoir. It would almost appear, however, that 

 by " tissue " Ehlers understands the " hardened sarcode " or 

 the so-called horny substance of the keratose sponges. Of 

 the supposed new form of sponge [Aulorkipis elegans), upon 

 which Ehlers founds his whole argument, he knows nothing 

 except the horny skeleton, no trace of soft parts. But this 

 horny skeleton, which encloses foreign bodies, is a solid cordj 

 attached to a worm-tube at one end, and the dichotomously 

 divided branches of Avliich spread out like a fan in one plane. 

 It is very probable tliat this skeleton does not belong to a 

 sponge at all. But should it be the product of a sponge, at 



* Ann. & Mag. N. H. 1870, 4t]i ser. vol. vi. p. 86. t Ibid. p. 250. 



\ " Anlorhipis cleqans, eine neue Spongien-Forni," Zeitschr. fiir wiss. 

 Zool. Bd. xxi. 1871 ; p. 540, pi. 42. 



§ The body-cavities of the sponges are placed by Ehlers in two diflerent 

 divisions. He calls " that great cavity of a sponge which has originated 

 by the development of a section of the calenteric space a me<iacalon, and 

 its orifice a mcyastomn ; but the inner space, which has originated by the 

 equal participation of the whole tissue of the s^yom/e, a ca-toma, and its entrance 

 a canostoma." According to my notion, the cavity which Ehlers indicates 

 as a mef/acoelon with a meyastoma will generally correspond "with the 

 stomach (yaster) with the vioitth-openiny {oscithitn). On the other hand, 

 the cavity which Ehlers names ca^loma will generally represent that part 

 of the intercanal system which I have named pseudogastir, and the cwno- 

 stoma of the former the psnidosfoma of the latter. It is, however, quite 

 incomprehensible how Ehlers can regard the cavities of the sponges as 

 partly cadenteric and partly non-ccelenteric, seeing that his entire memoir 

 is directed against the coelenteric interpretation of the canal-system of the 

 sponges, and at its close he expressly says : — " According to my concep- 

 tion, it is no longer open to discussion that the Sponges have no close 

 relationship to the Coelenterata." 



