ZOOLOGY AND BOTANY, MICROSCOPY^ ETC. 707 



tion cavity, and surrounded by a zona pellueida. The next stage, with 

 64 cells, is also without distinct cavity, and is somewhat elongated and 

 curved. When segmentation is complete, a simple layer of cells with 

 large nuclei is seen close under the zona pellueida. This corresponds to 

 what Rauber described in other rodents as the " Deckschicht." It incloses 

 a cavity filled with fluid, in which lies the mass of germinal cells. In 

 the latter hints of separation into ectodermic and endodermic layers were 

 discernible. 



In the next stage the endoderm cells begin to broaden out as a lining 

 of Eauber's sheath, while the ectoderm lies as a connected mass at one 

 pole. The modification of the free germinal mass into a germinal 

 cylinder closely united with the uterus, the invagination of the germinal 

 layers, the changes in Eauber's sheath, &c., are discussed, and Biehringer's 

 results corroborate those of Kupffer and Selenka. The inversion of the 

 germinal layers in rodents is essentially similar in all forms yet inves- 

 tigated, but the genera vary in details. Cavia stands by itself ; Mus 

 musculus, M. sylvaticus, and M. decumanus form a group ; while the 

 inversion in Arvicola amjpMhius most closely resembles that of A. arvalis. 



Spermatogenesis of Mammals.* — Prof. V. v. Ebner calls attention 

 to a research by Prof. E. Sertoli f on the spermatogenesis of the rat, 

 which appears to have been overlooked by many. Division was observed 

 only in the movable cells, and that always in definite periodic order, as 

 von Ebner has corroborated. The " nematoblasts " or sperm-cells have at 

 first nuclei which remain unstained by safranin, and only gradually 

 exhibit this property. 



Spermatogenesis in Guinea-pig.| — Sig. F. Sanfelice has studied the 

 regeneration of the testicular cells in the guinea-pig. The testicle 

 regenerates, not from the interstitial substance, but from the pre-existent 

 epithelium. The germinal cells (" cellules fixes " of Sertoli, " cellules de 

 soutien " of Merkel) take part in this regenerative process. 



Irritability of Spermatozoa of Frog.§ — Dr. J. Massart gives an 

 account of some observations made with the object of demonstrating the 

 irritability of the spermatozoa of the frog. They are preparatory to a 

 future demonstration of how sensitiveness to touch aids in the penetration 

 of the spermatozoon into the ovum. 



Development of the Axolotl.|l — MM. F. Houssayand Bataillon give 

 an account of the formation of the gastrula, of the mesoblast, and of the 

 notochord in the Axolotl. About twenty hours after deposition the egg 

 consists of a sphere with two poles ; one is black and made up of small 

 cells, the other is a clear grey, and is formed of larger cells. Between 

 these there is a segmentation cavity, but there is not yet any radical dis- 

 tinction between the two kinds of cells. The epiblast is, indeed, derived 

 from both the large and the small cells, the whole peripheral layer of the 

 egg differentiatiag and separating itseK from the subjacent cells. After 

 a little the epiblast divides into two layers ; this is in accordance with 

 the views of Scott and Osborn, who regard the jDossession of a unilaminate 

 epiblast as a primitive condition among the Urodela. It is clear from 



* Arch. f. Mikr. Anat., xxxi. (1888) pp. 424-5. 



t Rend. E. Istit. Lomb., xviii. fasc. 16, and Arch. Ital. Biol., vii. (1888) p. 369. 



j Arch. Ital. Biol., ix. (1888) pp. 425-6. Rev. Internaz. Napoli, 1887, 1 pi. 



§ Bull. Acad, R. Sci. Belg., Ivii. (1888) pp. 750-4. 



II Comptes Rendus, cvii. (1888) pp. 434-6. 



