TABLE OF ILLUSTRATIONS. 



PLATE I. 



FIG. 



1. Spermatozoa of Man ; A, viewed on the surface; u, viewed edgeways ($ 731). 



2. Vesicles of evolution from the seminal fluid of the Dog; A, B, c, single vesicles 



of different sizes; D, single vesicle within its parent-cell; E, parent-cell inclos- 

 ing seven vesicles of evolution ($ 732). 



3. Development of Spermatozoa within the vesicles of evolution ; A, B, vesicles con- 



taining spermatozoa in process of formation ; c, D, spermatozoa escaping from 

 the vesicles (| 732). 



[The three preceding figures are after Wagner and Leuckardt (Cyclop, of Anat- 

 omy and Physiology, Art. " Semen ").] 



4. Thin slice of the ovarium of a Sow three weeks old, showing the Graafian vesicles 



or ovisacs imbedded in a fibro-cellular stroma. The ovisacs are filled with 

 cells, in the midst of which one large one may be especially distinguished > 

 this, which is the germinal vesicle, is surrounded by minute granules, which 

 constitute the first indication of the yolk ( 737). 



5. Ovum of a Rabbit, showing the vitelline mass almost entirely converted into dis- 



tinct cells, of which those at the surface are pressed against each other and 

 against the zona pellucida, so as to assume a hexagonal form. The dark por- 

 tion consists of a mass of vitelline spheres, which has not undergone this con- 

 version (g 776). 



6. Ovum of the Rabbit, seven days after impregnation, viewed on a black ground. 



The outer membrane is the chorion, on which are seen incipient villosities. 

 Within this is the blastodermic vesicle, at the summit of which is the projec- 

 tion formed by the area germinativa ; and from this, the mucous layer of the 

 germinal membrane is seen to extend over about one-third of the surface of 

 the contained yolk ($ 776). 



7. Portion of the germinal membrane, taken from the area germinativa, to show the 



two layers of which it is composed ; the serous, or animal layer (epiblast) is 

 turned back, so as to show the mucous or vegetative layer (mesoblast and hyp- 

 oblast) in situ. In the latter is seen the primitive trace ( 776). 



8. Portion of the serous layer of the germinal membrane, highly magnified ; showing 



that it is made up of nucleated cells, united by intercellular substance, and 

 filled with minute molecules ( 776). 



