( 173 ) 

 SUMMARY 



OP CURRENT RESEARCHES RELATING TO 



ZOOLOaY AND BOTANY 



(principallt/ Tnvertehrata and Cryptogamia), 



MICROSCOPY, &c., 



INCLUDING OEIGINAL COMMUNICATIONS FROM FELLOWS AND OTHERS * 



ZOOLOGY. 



A. GENEBAL, including- Embryolog'y and Histology 

 of the Vertebrata. 



Germinal Layers and Early Development of the Mole.t— Mr. 



W. Heape gives the results of investigations upon the origin and 

 formation of the germinal layers in mammals, more especially in the 

 mole [Talpa Europcea), as follows : — 



1. The epiblast of the blastodermic vesicle owes its origin as 

 well to the inner mass of segmentation-spheres as to the outer layer 

 of segments. It appears to originate in two ways : — 



a. In the early stages of development (in the mole), probably by 

 the cells of the inner mass being directly transformed into part of the 

 wall of the blastodermic vesicle. 



6. In a later stage (mole and rabbit), by the transformation of the 

 rounded cells of the inner mass into a plate of columnar cells, which 

 joins the part of the outer layer immediately above it to form the 

 epiblast plate of the embryonic area. 



2. The mesohlast in the mole is formed in two portions : — 



a. A large portion, which has its origin in the primitive streak. 



h. A smaller portion, which is derived from the hypoblast situated 

 in front of the primitive streak. 



The author was unable to distinguish where the latter, or hypo- 

 blastic mesoblast, comes into contact with the mesoblast of the 

 primitive streak, and what part these respective layers take in the 

 future development of the embryo. 



3. A neurenteric canal is present in the mole similar to that formed 

 in other types of Vertebrata, first appearing as a pit at the anterior 

 end of the primitive streak, while in later stages it perforates the floor 

 of the hinder end of the medullary groove. 



* 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 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 tlie authors. 

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



t Proc. Roy. Soc, xsxiii. (1881) pp. 190-8. 



