158 SUxMAIAKY OF CURREXT RESEARCHES RELATING TO 



Spermatogenesis in the Orvet. — A. Dalcq {Comptes Re?idus Soc. 

 Biol. l'J20, 83, 995-7). The apparently similar sperroatids have 

 a hidden dimorphism, for some of them show a heterochromosome 

 which the others lack. This corresponds to what has been observed 

 in various insects and mammals. J. A. T. 



Post-natal Development of Rat's Ovary. — Hayato Arai {Amer. 

 Journ. Allot., 1920, 27, 405-62, 4 charts). The total number of ova 

 in both ovaries was counted in tliirty-nine albino rats, ranging in age 

 from birth to 947 days. In relation to the body-weight the size of the 

 ovaries increases to a maximum of 33 grm., thereafter it decreases 

 up to puberty, after which it increases rapidly and reaches the 

 second maximum. The ovary weight according to age shows continuous 

 increase up to thirty-one months. The weight of the right ovary is less 

 tban that of the left — about 90 p.c. — while the total number of ova is 

 slightly more in the right ovary. The total number of ova in both 

 ovaries decreases rapidly from 35,100 at birth to about 11,000 at twenty- 

 three days. From twenty-three to sixty-three days the number is 

 nearly constant (11,000 to 10,000). It then decreases again rapidly to 

 about 0,000 at seventy days. During the last period ovulation usually 

 occurs. From seventy days up to thirty-one months there is a slow 

 decrease to about 2,000 ova. In general, this decrease results mainly 

 from the degeneration of the primitive ova, but in part from that of the 

 definitive ova. 



With the increasing weight of the ovary the total number of ova 

 decreases. The increase in weight is associated before puberty princip- 

 ally with the formation of large degenerate follicles together with mature 

 follicles and growth of connective tissue, but after puberty the increase 

 depends mainly on the accumulation of small corpora lutea in addition 

 to the mature and degenerate follicles and connective tissue. After 

 puberty the number of large corpora lutea is about the same in all 

 ovaries, and these, therefore, are not responsible for the regular age 

 changes in the weight of ovaries. The new formation of the ktgg^ cells 

 takes place after birth from the germinal epithelium. These ova grow 

 in Fitu, and, as development proceeds, are covered by the adjacent 

 epithelial cells and extend into the stroma, passing through the tunica 

 albuginea. From these newly formed germ-cells the definitive ova 

 appear to develop, beginning from about the second week after birth. 

 The primitive ova, which are present during foetal life, are found degene- 

 rating immediately after birth. After puberty the degenerate follicles 

 are derived principally from the definitive ova. The mean number of 

 all degenerated follicles is about 10 p.c. of the total number of ova. 

 Ovulation can occur spontaneously, indei^endent of sexual intercourse 

 and without the influence of the male. The corpora lutea formed in 

 rats in which the ova have been fertilized are a little larger than those 

 in non-fertilized rats. Near maturity there may be as many as twenty- 

 one follicles in both ovaries. J. A. T. 



Development of Mammalian Spleen.— G. A. Thiel and H. Doavney 

 {Amer. Journ. Aaat., 1921, 28, 279-339, 3 pis., 3 figs.). The spleen 

 of white rat, pig and gopher is first seen as a dense mass of mesenchy- 



