DEPARTMENT OF EMBRYOLOGY. 91 



of the menstrual period, but the work of Meyer and Ruge completely 

 overthi'ows this theory. According to the latter, ovulation occurs 

 some time during the first 14 days of the menstrual month, a theory 

 which coincides with that of Dr. Mall. 



Regarding fertiUzation, resort is had to both comparative and 

 clinical studies, and the conclusion is drawn that the fertiHzing power 

 of the sperm is of relatively short duration, shorter, probably, than 

 the fertihty of the ovum, and that therefore fertilization occurs 

 within 24 to 48 hours after ovulation. It seems likely that fertilization 

 takes place nearly always within the tubes, ovarian pregnancy being 

 extremely rare. The best clinical data point to a week of sterihty 

 before the onset of menstruation, and a fertile period of 15 days 

 following its cessation. The average time of conception is probably 

 about the tenth day, accepting one day as the time elapsing between 

 ovulation and fertilization. 



The Contributions to Embryology, a series of embryological papers 

 started by Dr. Mall and heretofore pubhshed under his editorship, 

 have been continued, and during the past year the following two 

 volumes have appeared : 



Publication No. 227 (Contributions to Embryology, Vol. VII) : 



No. 20. The histogenesis and growiih of the otic capsule and its contained periotic tissue- 

 spaces in the human embryo. By George L. Streeter. 



21. The genesis and structure of the membrana tectoria and the crista spiralis of the 



cochlea. By O. Van der Stricht. t 



22. Study of a human spina bifida monster with encephaloceles and other abnormal- 



ities. By Theodora Wheeler. ^ 



23. A hvunan embryo before the appearance of the mj'otomes. By N. William 



IngaUs. 

 Publication No. 271 (Contributions to Embryology, Vol. VIll): 

 No. 24. The developmental alterations in the vascular system of the brain of the human 

 embryo. By George L. Streeter. 



25. The mitochondrial constituents of protoplasm. By E. V. Cowdry. 



26. The development and reduction of the tail and of the caudal end of the spinal 



cord. By Kanae Kunitomo. 



In connection with his studies on pathological embryos, undertaken 

 conjointly with Dr. Mall, important observations have been made 

 by Professor Arthur W. Meyer concerning the process of hydatiform 

 degeneration. Two papers on this subject are now in press. Dr. 

 Meyer finds that, instead of being a rare condition, this is one of the 

 most common forms of degeneration of the chorion and constitutes 

 an important factor in the cause of abortion. Microscopical examina- 

 tion of 348 uterine and 106 ectopic specimens, classed in the Carnegie 

 Collection as pathological, yields the following results: Of the uterine 

 cases which were in a sufficiently good state of preservation to admit 

 of diagnosis, there are 113 (32.4 per cent) that show hydatiform 

 degeneration. In the 106 ectopic specimens 44 (41.9 per cent) present 

 the same condition. The incidence of hydatiform degeneration in 

 specimens containing normal embryos is not determined. It was 



