98 The Life-History of Insects 



cavities (fig. 6i AI) are formed in each segment; 

 these are the coelomic pouches, and in most animals 

 (Vertebrates for instance) the body cavity of the adult 

 is formed by the extension and fusion of these primi- 

 tive pouches. Such a body-cavity is a true coelom. In 

 Arthropods and Molluscs, however, the coelom be- 

 comes much reduced as growth proceeds (6o, 6l). 



Fig. 62. — Cross sections through abdomen of German Cockroach embryo. A. 

 (later than fig. 61), magnified 100 times. B. (still more advanced, dorsal 

 closure complete), magnified 72 times, ec. ectoderm ; en. endoderm ; sp. 

 splanchnic layer of mesoderm ; y. yolk ; //. heart ; /. pericardial septum ; c. 

 coelom ; g. germ-cells surrounded by rudiment-cells of ovarian tubes ; in. 

 muscle-rudiment ; n. nerve chain \ /. fat body ; j. inpushing of ectoderm to 

 form air-tubes ; x. secondary body-cavity. After Heymons, Zeit. wiss. 

 Zoolog., vol. 53. 



Its development has been traced in the Cockroach 

 (62). Each coelomic pouch divides into three parts, 

 of which the dorsal contains the rudiments of the 

 genital organs, the central disappears, and the ventral 

 loses its boundaries as it becomes filled with the 



