SUMMARY OF CURRENT RESEARCHES. 167 



stroma. The adult interstitial gland develops in mole and weasel at the 

 expense of the elements of the internal theca ; but after these elements 

 are transformed into a special organ, the atresic corpus luteum. In the 

 weasel the cells of this organ are not changed except in form and arrange- 

 ment ; in tlie mole, follicles appear analogous to those of the foetal inter- 

 stitial gland. These are probably formed at the expense of epithelial 

 strands of the ovigerous substance, representing aborted tubes of Pfliiger. 

 In woman, besides the corpora lutea of menstruation and pregnancy, 

 there are atresic corpora lutea. The former develop from the granu- 

 losa ; in the latter the theca plays the chief part. The true corpora lutea 

 of the mole develop especially from the granulosa and in part from the 

 theca. They persist for some time after the end of gestation. 



Spermatogenesis in Hybrids.*— H. Poll enquires into the condition 

 of the testes in hybrid ducks {Cairina moschata and Anas boschas) and 

 in year-old mules, and compares the spermatogenetic (or pre-spermato- 

 genetic) proce8«es with what is seen in the pure stock. The general 

 result is that up to a certain point the processes in the hybrid are 

 essentially like those in the pure type. But when it comes to the de- 

 velopment of effective reproductive cells — functional spermatozoa — the 

 processes in the hybrid testes fail. 



Secretion of Accessory Reproductive Glands in Male Mammals.j 

 E. Iwanov has been led by experiments to conclude that the main 

 function of the accessory male reproductive glands is to supply a diluting 

 medium for the spermatozoa, whereby they can pass more readily from 

 the urethra and be forcibly injected into the vagina. Furthermore, in the 

 secretion of the prostate there are elements with an apparently fermen- 

 tative function. These seem to increase the locomotor energy of the 

 spermatozoa, and to shorten their length of life. 



Reproduction in Brown Rat.J — Newton Miller seeks to give more 

 precision to our knowledge of the reproduction of this common animal. 

 His results are based on the study of rats in captivity. The brown rat 

 breeds in every month in the year. The gestation period is 28i to 25J 

 days. The number of young in a litter varies from six to nineteen, 

 with an average of between ten and eleven. Five or six litters may 

 be reared by a single pair in a year. Seven litters were produced by 

 one female in seven months, and presumably, if the young are re- 

 moved or destroyed at birth, twelve litters might be produced in the 

 course of a year. There is very little courtship among brown rats. 

 Odour is important in sex recognition. Males fight persistently, and the 

 conquered avoid the victors. The females may and usually do resist the 

 males for a time, but they soon yield and lie passive. A female in full heat 

 is even more active than the male. Brown rats in captivity eat almost 

 50 p.c. of their young at birth. Most, if not all, are eaten by the females. 

 Full growth is not attained under eighteen months. Sexual maturity is 

 reached by both sexes not later t. an the end of the fourth month. 



* Arch. Mikr. Anat., Ixxvii. (1911) pp. 210-39 (1 pi. and 3 figs.), 

 t Arch. Mikr. Anat., Ixxvii. (1911) pp. 240 8. 

 % Amer. Nat., xlv. (1911) pp. 623-35 (2 figs.). 



¥ 2 



