102 THE ORIGIN OF PARASITES. 



from their earliest manifestation. Owing to the impossibility of 

 checking reasoning by experiment, all such attempts have a more 





FIG. 65. Embryos, A. of Curullanu*, and B. of titrongylus Jttaria. 



or less subjective character. It was not my intention to draw 

 up a phylogenetic tree for the parasitic Nematodes, since that 

 could be done only in reference to their relations, and might 

 prove illusory in a very short time. What I aimed at was not 

 more than to prove the possibility of such a relationship be- 

 tween the free-living and parasitic Nematodes as would clearly 

 allow of a derivation of the latter from the former, on the basis 

 of biological knowledge. 1 I will therefore also grant that the 

 connections may with equal, and perhaps even greater, right be 

 sought in other directions than that followed by me. Thus, for 

 instance, one might perhaps interpret the freely moving larviu which 

 I mentioned last as being allied to the Ithabditis-likQ condition of 

 other Nematodes, instead of explaining them to be only a subsequent 

 adaptation, as I endeavoured to do ; and one might, by the hypothesis 

 of one diminished function (merely of locomotion), derive them from 

 other Nematodes, and thus regard them in a certain way as degene- 

 rated Rhabditis-torms. But in fact this is somewhat deceptive, 

 especially when one considers larval forms of certain species of 

 Strongylidae, which, both by their organization and the systematic 

 position of their parents, remind us strongly of the JRhabditis-l&e 

 embryos of Dochmius and other Nematodes. Still, as above men- 

 tioned, these are only possibilities, and hence remain always arbitrary. 

 But thus much is established, that the parasitism of the Nematodes 



1 BUtschli has attempted in a similar way to prove the relations that exist between 

 the free-living and parasitic Nematodes. Bcricht d. Senkenb. naturf. GcaeUach., p. 56, 

 1872. 



