282 SUMMARY OF CURRENT RESEARCHES RELATING TO 



periphery, and pass through the nuclear transformations of ovogenesis, 

 becoming true ova. 



(Estrous Cycle in Dog.*— F. H. A. Marshall and W. A. Jolly point 

 out that the bitch is moncestrous, and has typically two sexual seasons 

 in the year, while the wild species in their natural state have only one 

 sexual season annually. The domestic cat has three or four sexual 

 seasons in the course of the year : it is polyoestrous, and may have four 

 heat-periods in a single sexual season ; the wild cat probably experiences 

 only one sexual season in the year. The lioness, failing pregnancy, may 

 have several annual sexual seasons, at the same time being polyoestrous ; 

 bears, polecats, and seals, and probably most other carnivores, appear to be 

 moncestrous and breed once a year, but the otter, in captivity at least, is 

 polyoestrous. The histological changes which the uterus undergoes 

 during the cycle may be divided into the following periods : — 



1. Period of rest .... anoestrum. 



2. „ growth and congestion . ) trum 

 ?>. „ destruction . . . J r 



4. „ recuperation 



oestrus. 

 ,metcestruni. 



Ovulation in the bitch takes place after external bleeding has been 

 going on for several days. It occurs during the period of oestrus, but 

 is quite independent of insemination. The hypothesis that the entire 

 procestrous process is of the nature of a preparation for the lodgment of 

 the ovum is in accordance with the facts. 



The authors note that no systematic investigation as to the vitality 

 of spermatozoa in mammals has been hitherto attempted, but they have 

 ascertained that the period of survival in the male passages of rabbits is 

 probably not more than ten days. 



Ovary as an Organ of Internal Secretion.f — F. H. A. Marshall and 

 W. A. Jolly conclude that the ovary is an organ providing an internal 

 secretion, which is elaborated by the follicular epithelial cells or by the 

 interstitial cells of the stroma. This secretion circulating in the blood 

 induces menstruation and heat. After ovulation, which takes place 

 during oestrus, the corpus luteum is formed, and this organ provides a 

 further secretion whose function is essential for the changes taking 

 place during the attachment and development of the embryo in the first 

 stages of pregnancy. 



Maturation-Divisions.:}: — Victor Gregoire has set himself the 

 laborious task of summarising the main results which have been reached 

 in regard to maturation-divisions in plants and in animals. Having 

 done so, he attempts a synthesis, or, where that is not possible, a 

 balance-sheet of the results. His general conclusion is, that in a large 

 number of cases the processes conform to one scheme, which lie calls 

 " heterohomeotypic." The gist of this scheme is as follows : — 



1. The two constitutive branches of the definitive chromosomes (i) 

 separate from one another in each chromosome at the first kinesis. 



* Proc. Roy. Soc, Series B, lxxvi., No. B 511 (1905) pp. 395-8. 

 t Loc. cit. * La Cellule, xxii. (1905) pp. 221-376. 



