EARLY STAGES OF DEVELOPMENT OP THE RABBIT. 121 



the cells of the four-segment stage^ and, as one would expect^ 

 it may appear that two segments are small and two larger, as 

 in fig. 6. 



Development between the 26th and 72nd Hours. 

 Stages of Segmentation between Four-Segment 

 Stage and Commencement of Cavity of the Blas- 

 todermic Vesicle. 



The further cleavage of the four segments does not occur in 

 each segment at the same moment. A stage of five segments 

 or even seven may often be found. 



In a rabbit killed 27-^ hours after coitus (Rabbit 36) I found 

 in the right Fallopian tube two ova in the usual locality for 

 this age, which is about 40 mm. above the uterus ; one of 

 them was in five segments, the other in seven. The five- 

 segment one is shown in fig. 7. 



In this specimen it will be seen that two (L^.) spheres are 

 almost exactly the same size, and that these are considerably 

 larger than two (S^.) of the remaining three, and slightly larger 

 than the third (S^.). This specimen I surmise may have been 

 one in which the two primary segments were unequal, and that 

 each of these divided into the approximately equal spheres^ 

 and that at the moment of examination one of the daughter 

 cells of the primary smaller (?) one had divided again into two 

 very nearly equal spheres (S^.). 



It should be noted that in van Beneden's account of the 

 process the larger primary segment gives rise to the more 

 rapidly dividing daughter cells forming his so-called epiblast ; 

 while in this case it seems to be the descendant spheres of the 

 smaller primary segment which appear to be the more ready 

 to undergo division. 



Fig. 14 is a camera lucida drawing of the other embryo of 

 the same Fallopian tube, seen as a transparent object. In 

 this specimen one segment {L~.) is larger than the others. The 

 four marked S^. were approximately equal, and slightly 

 larger than the two (L^-). May this be interpreted as follows? 

 The ovum which gave rise to this embryo divided into two 



