OR, MANUAI, OF THB APIARY. 97 



Straight, and curved (Fig. 39, a, b). Through the egg is an 

 opening (Fig. 41, A, B, m), the micropyle, through which 

 passes the sperm-cells. All insects seem to be guarded by a 

 wonderful knowledge, or instinct, or intelligence, in the pla- 

 cing of eggs on or near the peculiar food of the larva even 

 though in many cases such food is no part of the aliment of 

 the imago. The fly has the refined habits of the epicure, from 

 whose cup it daintily sips, yet its eggs are placed in the horse- 

 droppmgs of stable and pasture. 



Inside the egg wonderful changes soon commence, and 

 their consummation is a tiny larva. Somewhat similar 

 changes can be easily and most profitably studied by breaking 

 and examining a hen's egg each successive day of incubation. 

 As with the eggs of our own species, and of all higher ani- 

 mals, the egg of insects, or the yolk, the essential part— the 

 white is only food, so to speak-soon segments or divides into 

 a great many cells-in the morula stage-which soon unite into 

 three membranes, the blastoderms— blastula stage— which are 

 the initial animal ; these blastoderms soon form a single arch 

 or sac, and not a double arch, one above the other, as in our 

 own vertebrate branch. This sac, looking like a miniature 

 bag of grain, grows by absorption, becomes articulated, and 

 by budding out is soon provided with the various members. 

 At first the sixteen or seventeen segments are much alike, and 

 all bear appendages. From the three segments of the head 

 come the antenns and mouth organs, from the three thoracic 

 rings the three pairs of legs, while the remaining abdominal 

 joints generally soon lose all show of appendages, which are 

 never present in the imago. The trachea, and fore and hind 

 intestines, all but the stomach, are but invaginations of the 

 ectoderm or skin membrane, and so are shed when the skin is 

 moulted. As in higher animals, these changes are consequent 

 upon heat, and usually, not always, upon the incorporation 

 within the eggs of the sperm-cells from the male, which enter 

 the egg at an opening called the micropyle. The time it takes 

 the embryo inside the egg to develop is gauged by heat, and 

 will, therefore, vary with the season and temperature, though 

 in different species it varies from days to months. The num- 

 ber of eggs which an insect may produce is subject to wide 



