( 399 ) 

 SUMMAEY 



OP CURRENT BESEAKCHES RELATING TO 



ZOOLOGY AND BOTANY 



(principally Invertehrata and Cryptogamia), 



MICROSCOPY, &c., 



INCLUDING ORIGINAL COMMUNICATIONS FROM FELLOWS AND OTHERS.' 



ZOOLOGY. 

 A. VERTEBRATA :— Embryology, Histology, and General. 



o. Embryologry.f 



Origin of the Amnion.l — Mr. J. A. Eyder points out how, on a 

 mechanical principle, the amnion may have arisen during " develop- 

 ment of development." 



In those Teleostei in which the zona radiata closely surrounds 

 the ovum, the embryo becomes slightly pushed into the yolk, so that 

 a fold is produced at each end, which the author regards as a com- 

 mencement of the amniotic folds of higher forms. In those fishes in 

 which the zona is not so fii-m, the embryo can enlarge outwards, but 

 in others, as above, the embryo has to push its way into the yolk, 

 and partly takes its place as the yolk is absorbed. When, as in 

 mammals, there is no yolk in the yolk-sac, there is a greater space 

 for the embryo to be inpushed. The presence of a highly developed 

 brain necessitates an inpushing anteriorly, and gives rise to a more 

 marked and earlier " headfold." The amniotic folds never meet in 

 the Teleostei, because of the early escape of the embryos from the 

 egg, and also on account of the large amount of yolk which prevents 

 the complete inpushing. 



The author describes the mechanical cause of the inversion of the 

 layers in guinea-pigs, &c., which he regards as one extreme stage of 

 this series ; the Teleostei forming the opposite extreme. 



Germinal Vesicle-§ — M. C. van Bambeke discusses the various 

 opinions of v. Wielowiejski, E. Zacharias, and Ed. van Beneden, as 



* The Society are not intended to be denoted by the editorial " we," and they 

 do not hold themselves responsible for the views of the authors of the papers 

 noted, nor for any claim to novelty or otherwise made by them. The object of 

 this part of the Journal is to present a summary of the papers as actually published, 

 and to describe and illustrate Instruments, Apparatus, &c., which are either new 

 or have not been previously described in this country. 



t This section includes not only papers relating to Embryology properly so 

 called, but also those dealing with processes of Evolution, Development, and 

 Keproduction, and with allied subjects. 



X Araer. Natural., sx. (1886) pp. 179-85 (3 figs.). 



§ Bull. Acad. R. Sci. Belgique, xi. (1886) pp. 14-28. 



