ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 505 



period in the life-cycle. . . . The continuity of a hypothetic germ-plasm 

 resolves itself into an actual morphological continuity of germ-cells." 



CEstrous Cycle in Sheep and the Formation of the Corpus luteum.* 

 — F. H. A. Marshall makes a preliminary communication on this subject. 

 The ancestrum or resting period is from March to October ; in July 

 and August, for instance, the ovaries showed no protruding follicles, nor 

 corpora lutea, nor follicles begiuning to undergo atresia. Procestrum 

 and oestrus are hardly separable, and the two combined are short, 

 probably not more than two days. 



At the close of the anoestrum the vulva becomes swollen and con- 

 gested ; there is a slight flow of mucus ; in some cases there is ex- 

 tremely slight bleeding of the uterine wall. The characteristics of all 

 Heape's stages from I. to VI. were more or less clearly recognised in the 

 uterus. 



It was definitely shown that ewes need not be served in order to 

 induce ovulation, which indicates the possibility of successful artificial 

 insemination. When ovulation takes place, one follicle may rupture, or 

 one in each ovary, or two in the same ovary. 



The author has some notes on the period of " heat," the succeeding 

 rnetoestrum, and the period of rest (dioestrum). After not many days, the 

 dioestrum is followed by another procestrum, and so on, until the sheep 

 becomes pregnant or the breeding season is over. The complete 

 dioestrous cycle observed was 15 days, but other observations suggest 

 variation from about 13 to 18 days. 



Marshall gives an account of the development of the corpus luteum 

 which agrees substantially with that given by Sobotta for the mouse and 

 the rabbit, and by Stratz for Tupaia and Tarsius. It differs from 

 Sobotta in the description of the part played by the theca externa, and 

 in recording the not infrequently observed multiplication of the epithe- 

 lial cells by mitotic division in the earlier stages. It is entirely opposed 

 to the views of His, Kolliker, Nagel, Clark, Kabl, and Dcering, who all 

 more or less clearly describe the corpus luteum as an entirely con- 

 nective-tissue structure. 



Cleavage of Frog's Ovum. J — Fr. Kopsch finds (1) that in the egg 

 of Bana fusca there is no strict, but only approximate, correspondence 

 between the plane of the first cleavage and the median plane of the 

 embryo ; and (2) that in B. fusca, B. esculenta, and Siredon pisciformis, 

 the second cleavage does not separate cranial and caudal areas, nor the 

 third cleavage dorsal and ventral areas; for the dorso-ventral and cranio- 

 caudal axes of the embryo are not fixed until the end of the gastrulation. 

 These results are obviously not in agreement with those of most 

 other observers. 



Division of Spermatocytes in Mammals4 — Prof. V. von Ebner finds 

 that m the rat the first division is heterotypical and the second homo- 

 typical, the divisions occurring much as described by Meves for the 

 salamander. There is no evidence that a reducing division in Weis- 

 xuann's souse occurs, especially in view of the fact that a period of rest 



* Proc. Roy. Soc, Ixviii. (1901) pp. 135-40. 



t Internat. Monatschr. Anat. Physiol., xvii. (1900) pp. 1-26 (1 pi. and 5 figs.). 



I SB. Akad. Wisa. Wien, cviii. (1S99) pp. 429-48 (1 pi.). 



