444 ON GENERATION. 



defend themselves against the attacks of others ; she has coun- 

 terbalanced the shortness of their own lives by the number of 

 their progeny. " Nature," says Pliny, 1 " has made the timid 

 tribes among birds more fruitful than the bold ones." All 

 generation as it is instituted by nature for the sake of perpetu- 

 ating species, so does it occur more frequently among those 

 that are shorter-lived and more obnoxious to external injury 

 lest their race should fail. Birds that are of stronger make, 

 that prey upon other creatures, and therefore live more securely 

 and for longer terms scarcely lay more than two eggs once a 

 year. Pigeons, turtle and ring-doves, that lay but a couple of 

 eggs, make up for the smallness of the number by the fre- 

 quency of laying, for they will produce young as often as ten 

 times in the course of a year. They therefore engender greatly 

 although they do not produce many at a time. 



EXERCISE THE SIXTIETH. 



Of the uses of the yelk and albumen. 



" An egg/' says Fabricius, 2 " properly so called, is composed 

 of many parts, because it is the organ of the engenderer, and 

 Galen everywhere insists on the constitution of an organ as im- 

 plying multiplicity of parts." But this view leads us to ask 

 whether every egg must not be heterogeneous, seeing that every 

 egg is organic ? And every egg, indeed, even that of the fish 

 and insect, appears to be composed of several different parts, 

 membranes, coverings, defences ; nor is the included matter by 

 any means without diversity of constitution in different parts. 



Fabricius agrees farther, and correctly, with Galen, when he 

 says : 3 Some parts of the egg are the chief instruments of the 

 actions that take place in it, others may be styled necessary, 

 without them no actions could take place ; others exist that the 

 action which takes place may be better performed ; others, in 

 fine, are destined for the safety and preservation of all of these." 

 But he is mistaken when he says : " If we speak of the prime 



1 Lib. x, cap. 52. 2 Op. supra, id. p. 47 . a Ib. p. 48. 



