SEGMENTATION OF THE OVUM OP THE SHEEP. 207 



When the ova have reached the uterus, which is usually early 

 on the third day, the surest way of finding them is the adop- 

 tion of the method I made use of in the acquisition of the 

 early embryos of the pig. A ligature was placed round the 

 lower ends of the Fallopian tubes, a cannula was inserted and 

 tightly tied into the mouth of the uterus, both horns of which 

 were then slowly filled with '25 per cent, or "5 per cent, 

 chromic acid. 



The uterus, when distended to its uttermost and its lower 

 end ligatured, was left in chromic acid of the same strength 

 for one to three days. 



The contents were then let out and the uterus thoroughly 

 washed, and the contents and washings were searched through 

 under the microscope. 



This is an excessively tedious process, because during the 

 fourth to seventh days the uterus contains more or less of a 

 milky secretion, which renders the contents turbid, and greatly 

 increases the difficulty of finding so small an object as the 

 mammalian ovum. 



In this way about three out of five may be obtained. 



I received the uteri about three quarters of an hour to one 

 and a half hours after the death of the sheep, and filled them 

 at once with chromic acid. 



The specimens thus obtained were stained in carmalum, 

 hsemalum, Kleinenberg's hsematoxylin, or borax carmine, and 

 passed through the usual grades of alcohol, and through cedar 

 oil into paraffin and cut into series of sections, which varied 

 from '005 mm. to '01 mm. in thickness. 



The dates which I give are only approximate. I am not 

 sure that there is so much variation in the time that may 

 elapse between the moment of sexual union and fertilisation as 

 in the case of the pig. It is, however, very difficult to obtain 

 any one given stage. Circumstances did not permit of a con- 

 tinuous watch being kept upon the flock of sheep. The dates 

 which I give are not from my own observations, but are derived 

 from the information given me by the shepherd. 



For the purpose of this paper I killed forty-one sheep, and 



