359 



SUMMAEY OF CURKENT RESEARCHES 



BELATING TO 



ZOOLOGY AND BOTANY 



(PEINCIPALLY INVEETEBRATA AND CRYPTOGAMIA), 



MICROSCOPY, Etc.* 



ZOOLOGY. 



VERTEBRATA. 



a, Embryologry, Evolution, Development, Reproduction, 

 and Allied Subjects. 



G-erminal Vesicle in Cryptobranchus. — Bertram G. ^wit^ {Report 

 Michigan Acad. Sci., 1916, 17, 73-5, 1 pL). In the ovum about to 

 leave the ovary of this amphibian, the vicinity of the nucleus shows 

 opaque white globules readily visible to the naked eye. They seem to 

 be not nucleoli, as was at first supposed, but " yolk-islands," i.e. small 

 masses of yolk that become imprisoned between the vitelline membrane 

 and the germinal vesicle when the latter approaches the surface. The 

 subsequent dissolution of the germinal vesicle takes place not at the 

 very surface, but at a short distance from it. During recession a 

 trail of cytoplasm is left between the germinal vesicle and the animal 

 pole. In some ova the germinal vesicle appears to be in a state of 

 disintegration without ever having reached the animal pole, as shown by 

 the absence of this trail of cytoplasm. The dissolution takes place by 

 a gradual disintegration and convergence of its membranes. The 

 germinal vesicle usually collapses before the ovum escapes from the 

 ovary. J. A. T. 



Early Development of Opossum. — J. P. Hill {Quart. Journ. Micr. 

 Sci., 1918, 63, 91-139, -4 pis.). Observations were made on the early 

 stages of Didelphys aurita, and confirm the view that there is one 

 common mode of early development characteristic of the Didelphia as a 

 group. Cleavage, in the absence of a morula-stage, results in the 

 formation of a unilaminar blastocyst, the wall of which consists of 

 opposite polar areas of formative and non-formative regions. The 

 former is destined to furnish the embryonal ectoderm and the entire 



* The Society does not hold itself responsible for the views of the authors 

 of the papers abstracted. The object of this part of the Journal is to present 

 a sunamary of the papers as actually published, and to describe and illustrate 

 Instruments, Apparatus, etc., which are either new or have not been previously 

 delscribed in this country. 



