162 



AN INTRODUCTION TO ZOOLOGY 



passes out through the genital pore. The chitinous eggshell 

 prevents the digestion of the egg within the intestine of the host. 



int 



loll 



7TV 



FIG. 82. Transverse section of Ascaris lumbricoides. en., cuticle; dL, 

 dorsal line; der. epthm., epidermis; ex. v., excretory tube; int., intes- 

 tine; lat. I., lateral line; m., muscular layer ; ovy., ovary ; /., uterus; 

 v. v., ventral line. (From Parker and Haswell after Vogt and Yung.) 



The relations of the various organs to one another, as well as 

 the structure of the body wall, and the character of the ccelom, 

 are shown in Figure 82, which is a transverse section of a female 

 specimen of Ascaris lumbricoides. The body of the worm should 

 be considered as consisting of two tubes, one, the intestine (int.), 

 lying within the other, the body wall; while between them is a 

 cavity, the ccelom, in which lie the reproductive organs (ovy. and 



*.). 



The body wall is composed of several layers, an outer chitinous 

 cuticle (cu.), a thin layer of ectoderm (der. epthm.) just beneath it, 

 and a thick stratum of longitudinal muscle fibers (m.), mesodermal 

 in origin, lining the ccelom. Thickenings of the ectoderm form 

 the dorsal (d. 1), ventral (v. v) and lateral (lat. I) lines. In each 



