568 THE ANATOMY OF INVERTEBRATED AXIMALS. 



candra raphcmiis, there is a layer of flattened cells external 

 to the syncytium ; whence the latter may rather be regarded 

 as the equivalent of the mesoderm than of the ectoderm of 

 the Godenterata. And the observations of Barrois on other 

 calcareous sponges tend to the same conclusion. The care- 

 ful investigations of the last-named writer have not enabled 

 him to discover spermatozoa in any sponge, and he finds that 

 the ova, when they are first discernible, are situated in the 

 syncytium or mesoderm, and not in the endoderm. In the 

 free larvae of the calcareous sponges an equatorial zone of 

 rounded equal-sized blastomeres is interposed between the 

 ciliated, or epiblastic, and the nonciiiated, or hypoblastic, 

 hemisphere ; and it appears probable that these cells repre- 

 sent a mesoblast, and give origin to the mesoderm. The 

 embryo in this condition has a very interesting resemblance 

 to that of Clepsine^ in the stage in which the epiblast occu- 

 pies one face of the embryo, and the hypoblast, formed of 

 three very large blastomeres, the opposite face ; while an in- 

 complete zone of six or eight large blastomeres, which are 

 eventually inclosed by the epiblast, surrounds the margins of 

 the latter. 



At p. 135, I have quoted Haeckel's account of a pro- 

 cess of JEntogastric gemmation in Cannarina hastata of an 

 altogether anomalous character. 



F. E. Schulze ^ has lately investigated specimens of Gery- 

 onia hexaphylla provided with entogastric processes beset 

 with budding Giiniyim^ and he proves that, in this case, at 

 any rate, the phenomenon is one of parasitism. The stem 

 from which the buds proceed, in fact, is not a process of the 

 body of the Geryonia, but is simply attached to the wall of 

 the gastric chamber of the latter. It is hollow, and its cavi- 

 ty is lined by an endodermal epithelium. The Gunina buds 

 are not developed from the epithelium which covers the stem 

 and represents its ectoderm, but commence in the ordinary 

 way, as csecal diverticula of the wall of the stem, the apices 

 of which soon open to form the hydranth of a medusoid, the 

 disk of which results from the outgrowth of the base of the 

 hydranth. In all probability the larva of the Gunina enters 

 the gastric cavity of the Geryonia as a planula ; and, attach- 

 ino: itself to the wall, c:rows out into a stolon whence the me- 

 dusoids bud. 



^ "Ueber die Cuninen-Knospeniihren im Maeren v. Geryonien." (" Mit- 

 theilungen des Naturwissenschaftlichcn Vcreines." Gratz, 1875.) 



