TYPICAL THREADWORMS 



3421 



SPINY-HEADED THREADWORM a. Natural size; b. Head enlarged. 



TYPICAL THREADWORMS Order NEMATOIDEA 



The illustration showing the growth and structure of one of the threadworms 

 (Nematoxys], an internal parasite of the frog, is intended to show the mode of 

 development typical of the whole group. The egg is elliptical, and contains a mass 

 of granular protoplasm, the external wall of which soon becomes marked out into a 



FRONT END OE THREADWORM, Enoplus (much enlarged). 



layer of large cells. Meanwhile, there appears at the side a distinct notch or nick, 

 which, shallow at first, gradually deepens, until, as shown in the figures, it repre- 

 sents the space inclosed between the head and tail ends of the bent-up embryo, 

 which may be recognized respectively by their blunt and pointed extremities. The 



