NEMATODA. 



281 



the rectum, but finally pass to the exterior in the faeces, and so 

 reach the damp earth or muddy water, where they develop in a short 

 time into the Rhabditis-like forms, which have separate sexes and 

 are barely 1 mm. in length (Fig. 230, a and b). The impregnated 

 females of the latter produce only from two to four embryos, which 

 become free inside the body of the mother, pass into her body cavity, 

 and there feed on her organs, which disintegrate to form a granular 

 detritus. They finally migrate as slender, already tolerably large 



FIG. 230. a, Rhdbdonema (Ascaris) nigrovenosum, about 3'5 mm. in length, in the stage of 

 maturity of the male products ; G genital glands ; mouth ; D intestine ; A anus ; N nerve- 

 ring ; Drz glandular cells ; Z isolated spermatozoa, b, male and female Khdbditis forms from 

 about 1'5 mm. to 2 mm. long ; Ov ovary ; T testis ; V female genital opening ; Sp spicula. 



Nematodes into the lungs of the Batrachia, passing through the 

 buccal cavity and glottis. A similar alternation of parasitic forms 

 with free-living Rhabditis generations is presented by Rliabdonema 

 strongyloides (Anguillula stercoralis), parasitic in man (p. 290), and 

 by Bradynema mirabile (this is probably the real explanation of 

 Zur Strasse's observation, see p. 290). Khabdonema (Leptodera) 

 appendiculata, which lives in the slug Arion empiricorum, also 

 presents in its development a like alternation of heteromorphic 

 generations, which, however, are not strictly alternating, inasmuch 



