( 189 ) 

 SUMMAEY 



OF OUEKENT EESEAECHES EELATING TO 



ZOOLOaY AND BOTANY 



(principally Invertebrata and Cryptogamia), 



MICROSCOPY, &c., 



INCLUDING ORIGINAL COIIMDNICATIONS FEOM FELLOWS AND OTHERS * 



ZOOLOGY. 



A. GENEB.AL, including Embryology and Histology 

 of the Vertebrata. 



Development of the Ovum of Arvicola arvalis.f — The following 

 are the chief points of C. Kupffer's investigation into the alleged 

 reversal of the positions of the germ-layers in certain Rodents. 



1. The ovum of the field-mouse forms a normal blastoderm, show- 

 ing lamination in the region of the germinal disk, like the ovum of 

 the rabbit. 



2. The peculiarities of the field-mouse's ovum are caused by the 

 covering-layer, which, instead of disappearing, as in the rabbit's 

 ovum, proliferates and forms a plug which invaginates the active pole 

 of the ovum. It is this invagination, thus brought about by an 

 accessory growth, which causes the apparent reversal of the germ- 

 layers. 



3. With the exception of this invagination the course of develop- 

 ment is normal. A complete yolk-sac is produced, and, judging by 

 early stages, an amnion also, in the usual manner. 



4. The mesoderm appears in the neighbourhood of a swelling, 

 which is formed at a point in the periphery of the area embryonalis, 

 and is to be regarded as a csecal evagination of the ectoderm into the 

 cavity of the yolk-sac. This swelling may with great probability be 

 described as the commencement of the allantois. 



6. Although differences have already been known, to exist between 

 the field-mouse's ovum, after assuming the cylindrical form, and the 

 corresponding stage of the guinea-pig's ovum, it may nevertheless be 

 stated as certain that Bischoff was right in interpreting the whole of 

 the structure which he termed " plug " or " egg-cylinder," as an ovum. 



* The Society are not to be considered responsible for the views of the 

 authors of the papers referred to, nor for the manner in which those views 

 may be expressed, the maiu object of this part of the Journal being to present a 

 summary of the papers as actually published, so as to provide the Fellows with 

 a guide to the additions made from time to time to the Library. Objections and 

 corrections should therefore, for the most part, be addressed to the authors. 

 (The Society are not intended to be denoted by the editorial " we.") 



t SB. Miith.-phys. Kl. Akad. Wiss. Munchen, xii. (1882) pp. 621-37 (1 pi.). 



