RHABDITOID LARVAL FORMS. 



99 



tains in the uterus-like terminal portion of its generative organs an 

 innumerable quantity of Ehabditoid embryos, whicli become free by 

 boring to the exterior, and grow into mature males and females 

 without essential change of form. — E. L.^] 



But even the single example of Rliahdonema is sufficient not only 

 to place beyond doubt the special relations between parasitic and free 

 life, but to prove further that the former, instead of being collateral, or 

 even subsidiary to the latter, as in the case of Blidbditis appendiculata, 

 may, under certain circumstances, become more conspicuous ; the im- 

 portance of the free life, of course, becoming less in the same proportion. 



This alteration in the relative importance of the two conditions of 

 life has by no means reached its extreme point in Rhabdonema, for, 

 according to the above-mentioned (p. 61) researches, there is a whole 

 series of parasitic Nematodes (especially in the family Strongylidte), 

 among which the RhaMitis-iovm, instead of representing an indepen- 



FlG. 63. — Doc/imias trigcyiiocephaZus. A. Free-living young form ; 

 B. Young parasite. 



dent generation which precedes the parasitic, is limited to the young 

 stage of this latter, and passes on at once into the parasitic condition. 

 After the manner of the common Ehabditidse, these worms live at 

 first free in mud and damp earth, where they feed and grov/ until 

 they have attained a definite size. "With the shedding of their skin 

 the characters of the genus Rhabditis are lost, and also the possi- 

 bility of their former mode of sustaining life. The worms, however, 

 continue to live for some time imder the former conditions, but only 

 so long as the reserve material gathered in their interior is sufficient 

 to meet their necessities. In order to grow further, and to complete 

 their metamorphosis, they must exchange their former free life for a 

 parasitic one, and only in the interior of a living animal do they find 

 the conditions for their complete development. 



' The nbove passage lias been substituted by the author for one in the German edition. 



-w. E. H. Digitized by Microsoft® 



