FORM, GROWTH, AND CHANGE 29 



the limits of this book. 1 It must suffice to call attention to a 

 few outstanding facts of insect embryology which will be seen 

 to have a direct bearing on the later development subsequent 

 to the crisis of hatching 



Insects, like other members of the great arthropodan race, 

 produce eggs (Fig. 14 A) of large size. The egg of any animal 

 is always a relatively large cell in which an amount of food- 

 material for the nourishment of the developing embryo has 

 been stored up during the process of ripening. In certain 





FIG. 16. EGG-CASES OF VARIOUS INSECTS. 



I, Cricket (Oecanthus) ; 2, Butterfly (Oeneis) 3, Bug (Piezo- 

 sternum) ; 4, Pond-skater (Hydrometra). x 20. From 

 Comstock, " Introduction to Entomology ". 



groups, however, the mass of this food-material or yolk becomes 

 so great that the cell grows into a body easily visible without 

 any microscopic aid. An extreme case of such growth is 

 afforded by the familiar egg of a large bird ; here the egg, 

 properly so-called the overgrown cell is what is popularly 

 known as the " yolk " ; the " white," the membrane, and the 

 shell are to be regarded as a series of successively formed enve- 

 lopes. Insects, being small animals, cannot produce eggs that 

 are absolutely very large, but relatively to the size of the parent 

 a typical insect egg is large, while compared with the egg of a 



1 R. Heymons : " Die Embryonalentwicklung von Dermapteren und 

 Orthopteren". Leipzig, 1895. J. A. Nelson: "The Embryology of the 

 Honey-Bee ". Princeton, 1915. 



