CYTOLOGICAL CHANGES IX EGGS OF RAT. 317 



MATERIAL. 



For the material used in the preparation of this paper I am 

 indebted to Drs. J. A. Long and H. M. Kvans. I also wish to 

 express my thanks to Dr. Long for helpful encouragement. The 

 material was prepared for a study of ovulation in the rat, Mits 

 norwegicus. The females from which the ova were obtained 

 were isolated before parturition and kept from males thereafter, 

 thus preventing the po ibility of ova being fertili/ed. They 

 were killed at different intervals after parturition. The ovaries 

 and c\ id in t- \\eiv fixed iii Xenker's or in Benda'- fluid and .stained 

 in cannine, iron h.eniatoxylin, or phosphotungstic acid luenia- 

 \lin. The l.itit-r was by far the most useful -tain. The 

 I ; nl. i niateri.il v illy valuable for study of the c\ \< >pla-- 



mic (.lenient-, but it w.t- less useful than the Zenker preparation- 

 l"r detail- of nuclear -tincture, because the darkly -tainin:; 

 granule- .ind niitoc hondria tend to obscure the chromoMime- 

 e-pri ially in the period of scattering. In the fifty oviduct- 

 which were -tudied eggs were found in the di-tal portion in 

 t\\el\i in the middle upper portion in ten, in the lower- 



middle portion in -r\eii, and in the proximal portion in nineteen. 

 In all two hundred and fifty-two eggs were examined. As many as 

 nirit .uixl in some oviducts, but three, four, ,md h\e 



Were n- d nruch nnue commonly. 



OBSERVATION 



\t o\ ulaiion the -ei mid polar -pindlr lie- parallel to the periph- 

 ti\ of ilu- egg \\ith tin- d\ad- arranged upon it in t\-pical final 



prophase position. In any one oviduct all of the ova are al about 



the -aim- Stage. fable I. demonstrate- the fact that the com- 

 moner stages -ho\\ a natural -eiiieiice \\ith re-|u-ct to po-iiion in 

 the o\idtict be^inninv; \\ith di-tortioti of the -pindle and 5i 

 teiin- of the chi Mini - >me- and ending with the imei|iial fragmen- 

 tation of a multinucleate cell. It i- e\ident that \\ e are tlui- 

 pro\ idi-d with a natural -eriation of c\ tolo^ica cat 



value in interpretation of the re-nit.-. 



Stage I. It v ill be noted from Table I. th.it by far the great 

 number of ova found in the distal third of the oviduct \\ ere in the 

 nd polar- spindle stage. The -pindle may, however, be 

 -li-htly turned or even at right an^le- to it- original po-ition 



