116 RICHARD ASSHETON. 



derived the hypoblast and subsequently the mesoblast ; from 

 the descendants of the larger, the epiblast. 



As far as the conversion of the whole of the inner mass into 

 hypoblast and mesoblast is concerned, van Beneden has changed 

 his opinion, admitting that KoUiker's (and others — Balfour, 

 Heape) careful research in this matter is a truer account than 

 his own. 



Again, Heape, on the mole, has shown that a different inter- 

 pretation may be placed upon the fact as seen in the rabbit, 

 although he finds that there is a difference in the size of the 

 two first segments. 



The results of my researches show that there is, if not 

 always at any rate very frequently, a difference in size between 

 the first two segments ; sometimes the difference is very marked, 

 but more usually it is to be found only by careful measurement. 

 In one rabbit I examined the following results were obtained. 



K,abbit 48, was killed 24|^ hours after coitus. In the thin- 

 walled part of the Fallopian tube of the right side I found four 

 embryos at about 30 mm., 40 mm., 42 mm., 50 mm., from the 

 funnel mouth of the Fallopian tube respectively. 



No. 1, the highest up, had not as yet divided. The ovum 

 was spherical with a distinct nucleus, the ovum not occupying 

 the whole space within the zona radiata. 



No. 2, the second on the right side, was divided into two 

 segments, but this I did not measure. 



No. 3, the third and lowest on the right side, was also in two 

 segments. I could detect no differences at all in colour or 

 texture, but on measuring the longest and shortest diameters 

 of each the following results were obtained. 



One of the segments measured as follows : longest diameter 

 •1 mm., shortest diameter '076 mm. The other segment: 

 longest diameter '096 mm., and shortest "068 mm. 



The specimens were examined and measured in the fresh 

 condition in a drop of aqueous humour of the rabbit. The 

 measurements were taken with a micrometer eye-piece. No. 3, 

 and Zeiss D objective, which gave a magnification of t^^ ram. 

 for each division in the eye-piece. 



