Development and Metamorphosis 



born alive, after having passed a considerable time growing and developing 

 in the body of the mother. And this difference in degree of development at 

 birth is largely due simply to the difference in amount of nourishment 

 which can be afforded the young. The embryo in the egg uses up its food 

 early in its developmental career and before it has reached the stage of 

 likeness to its parents. It issues in a condition picturing some far-distant 

 ancestor of its species, or more frequently, perhaps, in a modified, adapted 

 condition, fit to make of this tender unready creature thus thrust before 

 its time into the struggle for living an organism capable of caring for itself, 

 although not yet endowed with capacities as effective as, or even similar to, 

 those of the parent. 



It is familiar to us, then, that development is not wholly postnatal or 

 postembryonic; that before birth or hatching a greater or less amount of 



development, requiring a longer or shorter 

 period of time, has already been undergone. 

 Every animal begins life as a simple cell; all 

 animals except the Protozoa (the simplest ani- 

 mals, those whose whole body for its whole 

 life is but a single cell) finish life, if red 

 Nature permits them to come through myriad 

 dangers safely to maturity, as a complex of 

 thousands or millions of cells united into 

 great variety of tissues and organs. This 

 great change from most simple, to most complex 

 condition constitutes development: the actual 

 increase of body-matter and extension of 

 dimensions is growth. 



Most insects hatch from eggs; being born 

 alive is the exceptional experience of the young 

 of but few kinds, and even this is a sort of 

 pseudo-birth. Such hatch alive, one may better 

 say, for they begin life in eggs, not laid out- 

 side the mother body to be sure, but held in 

 the egg-duct until hatching-time. With very few exceptions, young insects 

 are not nourished by the mother except in so far as she stores a supply of 

 yolk around or by the side of each embryo inside the egg-shell. The form- 

 ing of the egg is a matter which does not lend itself readily to the observa- 

 tion and study of amateurs, but is a phenomenon of unusual interest to 

 whomever is privileged to discover it. The insect ovaries consist of a pair 

 of little compact groups of short tapering tubes (Fig. 66). In the anterior or 

 beginning end of each tube is a microscopic space or chamber from whose 

 walls cells loosen themselves and escape into the cavity. These cells become 



od. 



FIG. 66. Ovaries and oviducts 

 of a thrips. o.t., ovarial tubes: 

 o.d., oviduct; r.s., seminal 

 receptacle, or spermatheca; 

 d.r.s., duct of the seminal re- 

 ceptacle. (After Uzel; much 

 enlarged.) 



