610 



UTERUS AND ITS APPENDAGES. 



the latter and the zona pellucida, which in- 

 terspace is filled by a transparent fluid, has 

 been noticed in many mammalia, as the 

 Guinea-pig, rabbit, &c. 



Fig. 412. 



The ovum a little more advanced in the tube. (After 

 Bischoff.) 



The surface is perfectly smooth. Spermatozoa 

 have penetrated the zona pellucida. The respira- 

 tory chamber is formed between the latter and the 

 yelk. The rotation of the yelk has commenced, as 

 indicated by the arrows. The granular bodies ap- 

 pear preparatory to the segmentation of the yelk. 

 Several of these stages are seen commencing in the 

 preceding figure. Rabbit, 



This change is preliminary to another oc- 

 currence, which has been observed in the 

 ova of many animals, both vertebrate and 

 invertebrate, viz. the rotation of the yelk 

 within the interspace just described ; a ro- 

 tation which is effected by the aid of cilia 

 clothing the surface of the yelk. 



About this time may be observed one, or 

 perhaps two, small granular bodies, whose 

 formation has given rise to many and varied 

 speculations regarding their signification and 

 use. They occupy a portion of the space 

 between the yelk and zona pellucida, and 

 appear to be common to the mammalian 

 ovum and that of other classes. The most 

 probable supposition regarding their use con- 

 nects them with the division or cleavage of 

 the yelk which follows their appearance. 



Whatever doubts may be entertained as to 

 the dependence of the phenomena already 

 described upon a preceding act of impregna- 

 tion, all question is set at rest at this point, 

 by the direct experiments of Newport, who 



Fig. 413. 



ascertained beyond doubt, that segmentation 

 of the yelk is the result of impregnation alone, 

 and that it never takes place in the unim- 

 pregnated ovum. 



This segmentation of the yelk consists in 

 a spontaneous cleavage of that body, at first 

 into two, and then into four, equal parts ; the 

 process of division continuing in geometric 

 progression until the whole is broken up into 

 a mass of finely nucleated particles, between 

 which the original sperm-force is probably 

 equally divided. 



Segmentation of the yelk of the mamma- 

 lian ovum has never been observed in its 

 commencing stages anywhere but in the tube. 

 The extent to which it proceeds beibre the 

 ovum quits the oviduct to enter the uterus 

 appears to vary in different species. Bischoff 

 never saw more than four yelk-divisions in 

 the ovum of the Guinea-pig by the time that 



Fig. 414. 



The ovum from the lower or uterine end of the 

 Fallopian tube. {After Bischoff.) 



The yelk exhibits four divisions. Babbit. 



it had reached the lower portion of the tube ; 

 and it is probable that a further division into 

 eight parts occurs in the extreme end of the 

 duct, since, in the next condition of the ova 

 found in the uterus, the yelk exhibited 12 

 16 divisions. 



The only remaining change in the condition 

 of the ovum during its residence in the ovi- 



Fig. 415. 



The ovum still more advanced in the tube. {After The addition of a layer of albumen in the lower por- 

 Bischoff.) tion of the tube (observed only in the rabbit.') 



(After Bischoff.) 



The first stage in the segmentation of the yelk 

 has taken place. Rabbit. 



The yelk exhibits eight divisions. 



