SUMMARY OF CURRENT RESEARCHES 



RELATING TO 



ZOOLOGY AND BOTANY 



(principally inveetebrata and cryptogamia), 



MICROSCOPY, Etc.* 



ZOOLOGY. 



VERTEBRATA. 



a, Embryolog-y.t 



Fission of Embryonal Area in Mammals. { — Richard Assheton 

 points out that the poly-embryony of Tatusia is due to fission, not to 

 budding, nor to separation of blastomeres. Fission of embryonic masses 

 is not unknown in other Mammals. Thus in a sheep a blastocyst has 

 been observed with two perfectly formed embryonal areas, which pro- 

 bably arose during the formation of the blastocyst from the morula 

 by accidental separation of ectodermal cells into two groups. In the 

 ferret some interesting conditions have been found in w^hich groups of 

 cells, like small morulse, occur between the zona radiata and the tro- 

 phoblast of the blastodermic vesicle, which suggest fission at an early 

 period. 



In the Edentates there is a peculiar combination of three conditions 

 not found in other Mammals : — (1) the formation of a blastocyst with 

 a large cavity free within the general lumen of the uterus ; (2) an 

 *' inversion of layers " ; and (3) a late thickening of trophoblast over 

 the embryonal area. It is suggested that a radial dispersion of the 

 ectoderm cells of the embryonal area has led to the normal produc- 

 tion of a number of embryos by fission of the peripheral ectoderm, the 

 more central .part thinning out owing to the presence of the tropho- 

 blastic thickening or its derivatives. 



Heterochromosomes in Mammals. § — H. E. Jordan notes that 

 heterochromosomes have been reported for the male germ-cells of 



* 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 puh- 

 lished, 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, Reproduction, and 

 allied subjects. 



X Resumes des Communications, 9e Congres Internat. Zool. Monaco, 1913, 

 ser. 3, pp. 18-19. 



§ Proc. Soc. Exp. Biol, and Med. x. (1912) pp. 20, 21. 



