Page:The Works of William Harvey (part 1 of 2).djvu/544

 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.