198 J. A. MYERS 



live more than nine or ten hours in the reproductive tract of the 

 female. 



During 1914-1915 a large immber of observations were made 

 on females with the hope of finding a definite way of knowing 

 just when the animals is in heat or when copulation has taken 

 place. No definite gelatinous plug was found closing the va- 

 ginal orifice after copulation as Sobotta ('95) observed in white 

 mice. A yellow and somewhat viscid vaginal secretion appears 

 at rather regular intervals. This secretion usually makes its 

 first appearance shortly after the opening of the vagina which 

 occurs about the eighth week. In young females it occurs 

 thereafter at quite irregular intervals but later it may be seen 

 about every fifth to eighth day. No definite relation has yet 

 been established between the appearance of the vaginal secre- 

 tion and the time of insemination. However, it was noticed 

 that many of the females became pregnant while the secretion 

 was present. The origin of the vaginal secretion and its relation 

 to ovulation is still being studied with the hope of obtaining 

 definite knowledge as to the time of ovulation in the white rat. 



Some of the fetuses were fixed in Zenker's fluid, others in 10 

 per cent formalin. In the earlier (fifteen day and nine hours, 

 sixteen day and twelve hours, and seventeen day and two 

 hours) stages several fetuses were cut for each stage described 

 while in the later (eighteen days and nine hours, nineteen days 

 and six hours, and twenty days and six hours) stages only one 

 fetus was entirely sectioned and merely the skin containing the 

 mammary glands from several other individuals was sectioned. 

 The mammary glands of other fetuses were studied macroscopi- 

 cally. In all 30 individuals were examined. A part of the ma- 

 terial was cut at 5 M or 7 M and stained with iron hematoxylin; 

 the remainder was cut at 10 /i and stained \vith alum hematoxylin 

 and eosin or with Mallory's connective tissue stain. Weigert's 

 elastic tissue stain was also applied to some of the fetuses of the 

 latest stages. For a study of the varieties of white blood cor- 

 puscles Dominici's combination stain was used. 



A few dissections and observations proved that in the late fetal 

 stages the sex could be determined by the relative ano-genital 



