Chap. 30 

 A 



ARTHROPODS INSECTS, SPIDERS, AND ALLIES 



B C D 



613 



fertilized egg 



cleavage 



blasfoderm 



germ band 



Fig. 30.19. Development of the grasshopper. Development begins in autumn 

 immediately after fertilization, and continues two to three weeks till the embryo 

 is well formed. Then there is a rest or diapause until spring when the nymphs 

 hatch at the right time to feed on the young grass. A, B, C, D; nuclear division 

 occurs and {B) nuclei are scattered through the yolk; they migrate to the outer 

 surface of the embryo where each one is surrounded by a cell body. This (C) is 

 the blastula stage. D, cells divide rapidly on one side forming the germ band 

 which will be the embryo. E, F, G, H, I; continuous development proceeding 

 most rapidly on the ventral side where the nerve chain will be located. Stomodeum 

 is the layout for the mouth; proctodeum is the layout for the anal region. The 

 serosa is the outer covering membrane of the embryo; the amnion is the inner one. 

 J, development pauses for the winter (diapause). K, L, M; development begins 

 again; the embryo turns about so that its head is at the larger end of the egg. It 

 soon hatches, head first. Like other immature animals its head is relatively large. 

 N, O, P, Q, R; five nymphal stages. S, adult. Legs came before wings in the evo- 

 lutionary history of insects; they come first in young grasshoppers. (Adapted from 

 various sources. Courtesy, Storer: General Zoology, ed. 2. New York, McGraw- 

 Hill Book Co., 1951.) 



