279 



SUMMAllY OF CXmEENT RESEAECHES 



RELATING TO 



Z (3 O L O G Y AND BOTANY 



(principally invertebrata and cryptogamia), 



MICEOSCOPY, Etc.* 



ZOOLOGY. 



VERTEBRATA. 



a. Embryology. t 



Development of Horse4 — J- Cossar Evvait has made a study of the 

 development of the horse during the third week. He begins with a 

 discussion of the previous work on young horse embryos by Bonnet, 

 Martiuj and Hausmann. A description is then given of the reproductive 

 organs and foetal membranes at the end of the third week. The external 

 characters, nervous system, sense organs, alimentary canal, notochord, 

 heart and blood-vessels of the three-weeks' embryo are then discussed. 

 The early developmental stages in the horse and the sheep are then 

 compared. 



From the second week onwards the horse follows a route of develop- 

 ment different from that of all the other Mammals hitherto studied. 

 There is no evidence that the development is arrested at any stage in 

 the horse, as it is in the roe deer, where after the cleavage stage is 

 reached little or no progress is made for several months. At the end 

 of the third week of gestation, the blastocyst measures 50 mm. The 

 trophoblast at the end of the third week differs in several essential 

 points from that of sheep and pig and other Ungulates hitherto examined. 

 There is a continuous sheet of nutritive coagulum between the tropho- 

 blast and the yolk-sac endoderm. In the vicinity of the embryo the 

 yolk-sac consists of endoderm and a layer of splanchnic mesoderm, but 

 from the exocoelom to the sinus terminalis it is only represented by 



* 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 pub- 

 lislied, and to describe and illustrate Instruments, Apparatus, etc., 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 Evolution, Development, Eeproduction, and 

 allied subjects. 



% Trans. Roy. Soc. Edinburgh, li. (1915) pp. 287-329 (10 pis. and 21 figs.). 



