THE EGG 



surface and the overlying capsule of the ovary become thinner 

 and thinner. The actual rupture of the follicle through the 

 thinned-out region has been observed repeatedly in rabbits 

 and sheep, following the lead of Walton and Hammond of 

 Cambridge, England (1928), and has been photographed in 

 motion pictures by Hill, Allen and Kramer of Yale Medical 

 School. It happens that in the rabbit these events in the ovary 

 can be timed very closely. The investigators anesthetize an 

 animal which is about to ovulate and expose one of its ovaries 

 under warm salt solution. Several ripening follicles are seen. 

 Watching or photographing one of these, they see the thin 

 exposed wall of the follicle weaken still more, until it bulges 

 to make a little bleb. Meanwhile the cells about the egg on 

 the inner wall of the follicle have loosened up so that the egg 

 is nearly free from its attachment. Finally the bleb rips open 

 and the contents of the follicle is expelled, carrying the egg 

 with it. In motion pictures, the ejection of the contents looks 

 like the slow rise and fall of a geyser; it is not explosive, but 

 actually rather a gentle occurrence. In animals like the rab- 

 bit, which produce several young at one time, the individual 

 follicles of one batch rupture within a few minutes of each 

 other. 



The egg. The eggs of mammals, seen under the microscope, 

 are beautiful little spherical objects, consisting of a round 

 mass of cellular material surrounded by a transparent zone 

 or membrane (Plate VII, D). The eggs of all the higher 

 mammals thus far measured have been not far from 0.1 

 millimeter (0.004 inch) in diameter. Mouse and rat eggs are 

 a little smaller (0.075 mm.), those of dog, cow, and human a 

 little larger (0.140 mm.). Dr. Carl G. Hartman suggests a 

 striking comparison by which we can appreciate their size, 

 relative to more familiar objects: "Scatter a pinch of sea 

 sand on a piece of black paper — the smallest grain visible to 

 the naked eye is of the order of magnitude of the cow's egg.^^ 



{ 37 } 



