314 SUMMARY OF CURRENT RESEARCHES RELATING TO 



SUMMARY 



OF CURRENT RESEARCHES RELATING TO 



ZOOLOGY AND BOTANY 



{principally Invertehrata and Cryptogumiu), 



MICROSCOPY, &c., 



INCLUDING ORIGINAL COMMUNICATIONS FROM FELLOWS AND OTHERS.' 



ZOOLOGY. 



A. GENERAL, including Embryolog-y and Histolog-y 

 of the Vertebrata. 



Germinal Layers of the Chick.f — Professor F. M. Balfour and 

 Mr. r. Deighton record the results of a renewed study of two much 

 disputed points in the ontogeny of birds, viz. the origin of the 

 mesoblast and the origin of the notochord. 



1. With reference to the first of these, their results are briefly as 

 follows : — 



The first part of the mesoblast to be formed is that which 

 arises in connection with the primitive streak. This part is in the 

 main formed by a proliferation from an axial strip of the epiblast 

 along the line of the primitive streak, but in part from a simul- 

 taneous difi'erentiation of hypoblast cells also along the axial line of 

 the primitive streak. The two parts of the mesoblast so formed 

 become subsequently undistinguishable. The second part of the 

 mesoblast so formed is that which gives rise to the lateral plates 

 of mesoblast of the head and trunk of the embryo. This part 

 appears as two plates — one on each side of the middle line — which 

 arise by direct differentiation from the hypoblast in front of the 

 primitive streak. They are continuous behind with the lateral wings 

 of mesoblast which grow out from the primitive streak, and on their 

 inner side are also at first continuous with the cells which form the 

 notochord. 



In addition to the parts of mesoblast, formed as just described, 

 the mesoblast of the vascular area is in a large measure developed 

 by a direct formation of cells round the nuclei of the germinal 

 wall. 



The mesoblast formed in connection with the primitive streak 



* 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 main object of this part of tlie Journal being to present a 

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

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

 corrections should tlierefore, for the Uiost part, be addressed to tlie authors. 

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



t Quart. Journ. Micr. Sci., xxii. (1882) pp. 176-88 (3 pis). 



