129] LIFE HISTORY OF GORDIUS AND PARAGORDIUS—MA Y 9 



The habits of different species are practically unknown. Most of the 

 material has been found accidentally as isolated specimens and observations 

 on behavior have been made mostly on animals in captivity as Wesenberg- 

 Lund has already pointed out. The scant observations made on animals 

 in nature are mostly referred to the group as a whole and not to any parti- 

 cular species. But there is no reason for supposing that the habits of 

 different species are the same, and they are not the same in the species 

 forming the subject of this paper. 



The problem of the life history of the group has attracted much atten- 

 tion. Villot at one time thought he had the complete cycle, but found later 

 that he had to modify his theories. He observed the embryological 

 development, the encystment of the larvae in a large number of animals, 

 and the presence of nearly adult worms in beetles. After holding for a long 

 time the view that the animals harboring the encysted larvae were inter- 

 mediate hosts he finally concluded that the encysted larvae perish and 

 that the life cycle is completed in some other way. Camerano indepen- 

 dently arrived at the same conclusion. Blunck (1915) again speaks of an 

 intermediate host. He states that the larvae of Gordius tolosanus penetrate 

 soft-bodied animals and these in turn are devoured by Dytiscus larvae. 

 Tadpoles form for the most part the intermediate host. Development is 

 completed in Dytiscus and the worms escape soon after the beetle emerges 

 from the puparium. The facts upon which these deductions are based are 

 not given. Nothing has been published on the metamorphosis or the 

 structure of the early parasite. In regard to the later organogeny Villot 

 (1891) and Vejdovsky (1894) have supplied the only information. 



The adult organization is better known. If the knowledge of it is still 

 incomplete, that is due chiefly to the fact that the material at hand has 

 often been scarce and the methods employed have given only poor results. 

 Here as elsewhere the greatest confusion has arisen because of the belief 

 that what is true of one species must be true for all. Writers have not 

 hesitated to denounce their fellow workers when their particular species 

 faUed to show what others had found in very different species. 



This very brief discussion of the literature on Gordiacea has been given 

 not with the purpose of presenting an historical account of the subject but 

 with the object of pointing out the need for further investigation and some 

 of the difficulties that have presented themselves. 



The present investigation was undertaken with the object of increasing 

 the knowledge of some of the common American Gordiacea. The chief 

 purpose was to trace out if possible the complete life cycle in one or the 

 other of the two species most easily available; special attention being given 

 to the host succession and the organogeny. 



The work was suggested in the fall of 1913 by Professor Henry B. 

 Ward, under whose direction it was carried on. To him I wish also to express 



