656 



REPRODUCTIVE ORGANS. 



portion of the tube situated in the wall of the uterus. 3. Infundib- 

 ular, in which the gestation develops in the outer end of the tube- 

 lumen or among the fimbria?. 4. Anomalous Varieties. Among 

 these Webster places those that develop in accessory fimbriated 

 extremities or in tubal diverticula, and also those that develop in 

 detached portions of Mullerian tissue i. e., those attached to or 

 embedded in the ovary. In this class, he thinks, are some of the 

 recently described cases of ovarian pregnancy. 5. Cornual preg- 

 nancy, in which the ovum develops in the undeveloped horn of a 

 bicornate uterus. 



zp. 



FIG. 440. Sections of the ovum of a rabbit, showing the formation of the blasto- 

 dermic vesicle : a, b, c, d, are ova in successive stages of development ; zp, zona pel- 

 lucida ; ect, ectomeres, or outer cells ; ent, entomeres, or inner cells (E. Van Beneden). 



Method of Fertilisation. In the vitelline membrane of 

 the ova of some animals there is a minute opening, the micropyle, 

 by which a spermatozoon gains access to the interior. Such an 

 opening does not exist in the human ovum. Some histologists 

 have described the vitelline membrane as possessing a porous 

 structure, and it has been suggested that through one of these 



