ON GENERATION. 243 



becoming diffused through it, (which is the cause of its spoiling,) 

 so do eggs perish when the yelk spoils, for the lees and the yelk 

 are the more earthy portion in each. Wherefore wine is destroyed 

 by an admixture with its dregs, and an egg by the diffusion of its 

 yelk." 1 And here, too, we may not improperly refer to that 

 passage 2 where he says : " When it thunders, the eggs that are 

 under incubation are spoiled ;" for it must be a likely matter 

 that a membrane so delicate should give way amidst a conflict 

 of the elements. And perhaps it is because thunder is frequent 

 about the dog days that eggs which are rotten have been called 

 cynosura ; so that Columella rightly informs us that " the 

 summer solstice, in the opinion of many, is not a good season 

 for breeding chickens." 



This at all events is certain, that eggs are very readily shaken 

 and injured when the fowls are disturbed during incubation, at 

 which time the fluids are liquefied and expanded, and their con- 

 taining membranes are distended and extremely tender. 



EXERCISE THE EIGHTEENTH. 



The fourth inspection of the egg. 



" In the course of the fifth day of incubation," says Aristotle, 3 

 " the body of the chick is first distinguished, of very small di- 

 mensions indeed, and white ; but the head conspicuous and the 

 eyes extremely prominent, a state in which they afterwards 

 continue long ; for they only grow smaller and shrink at a later 

 period. In the lower portion of the body there is no rudimen- 

 tary member corresponding with what is seen in the upper part. 

 But of the channels which proceed from the heart, one now 

 tends to the investing membrane, the other to the yelk; together 

 they supply the office of an umbilical cord. The chick, therefore, 

 derives its origin from the albumen, but it is afterwards nourished 

 by the yelk, through the umbilicus." 



These words of Aristotle appear to subdivide the entire gene- 

 ration of the chick into three stages or periods, viz. : from the 



1 Hist. Anim. lib. vi, c. 2. * Ih. lib. viii, c. 5. 3 Ib. lib. vi, c. 3. 



