ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 485- 



the regular sexual season, when the additional stimulation supplied by 

 coition may be necessary. In the ferret, ovulation does not occur in the 

 absence of coition, without which the follicles undergo atresia. 



In the sheep, atresia is commonest in follicles of about -J— h the 

 dimensions of the mature follicles. When it occurs with any con- 

 siderable frequency, it must affect the barrenness percentage in sub- 

 sequent breeding seasons. The atretic follicle differs from the developing 

 corpus luteum in the absence of any discharge to the exterior ; the 

 membrana granulosa degenerates and disappears prior to any considerable 

 ingrowth from the connective-tissue wall. 



As to the formation of the corpus luteum, the lutein cells are derived 

 from the membrana granulosa, while the connective-tissue element is 

 supplied by the proliferation and ingrowth of the thecal interna and 

 externa. Leucocytes are abundant, especially at the sixteenth-hour stage 

 of development, but these disappear in later stages without giving rise 

 to connective tissue as described by Sobotta. The cavity of the dis- 

 charged follicle is filled in by the further ingrowth of connective 

 tissue. 



Perhaps the most important result is the additional evidence as to 

 the identity of the two processes of pro-cestrum and menstruation. 



Yolk-Nucleus or Corpus Balbiani in Vertebrates.* — K. v. Skro- 

 bansky has studied this much discussed body in the ova of the guinea-pig. 

 The question is, whether it represents morphologically and genetically 

 a " sphere-apparatus " (idiozome, centrotheca, or centriole), or whether 

 it is a quite distinct structure. According to the author's observations, 

 the formation of the body is not associated with the division of the 

 oogonia, and the corpuscle cannot therefore be identified as a sphere- 

 apparatus. Herein he agrees especially with Gurwitsch. 



Determination of Sex.f — B. S. Schultze indicates that as long ago 

 as 1855 he maintained that sex was determined even before fertilisation. 

 It may be that the older the father is in relation to the mother, the 

 more male offspring there will be (Hofacker and Sadler). It may be 

 that a sire which functions frequently will have relatively more male 

 offspring than one which serves less frequently (the conclusion of many 

 breeders). But these conclusions are not antagonistic to the theory of 

 " progamic " determination. 



The "masculine ova" leaving the ovary of the young female may 

 have more attraction for the spermatozoa of the older male parent than 

 the " feminine ova " have. The " masculine ova " may attract sperma- 

 tozoa fresh from the testes more than the " feminine ova," which may 

 be relatively more accessible to spermatozoa which have been longer 

 in the testes. It is evident that there are many " may-be's " to be con- 

 sidered before this difficult problem can be regarded as scientifically 

 settled. 



Development of Spleen in Tropidonotus natrix.J — W. Tonkoff 

 has shown previously that in various Amniota the primordium of the 



* Arch. Mikr. Anat., lxii. (1903) pp. 194-206 (1 pi.). 



t Centralbl. f. Gynakol., 1903, pp. 1-4. See Zool. Centralis., x. (1903) p. 372 



% Anat. Anzeig., xxiii. (1903) pp. 214-6. 



