00 ILUNOIS BIOLOGICAL MONOGRAPHS [180 



nor truly herbivorous. There is then, so far as the habits of the hosts are 

 concerned, no reason why the infection should not take place as indicated 

 in the earlier papers of Villot and Camerano and in the reports of most other 

 •writers. But the later conclusions of Villot and Camerano did not agree 

 with the older views, neither do the results of the present investigation bear 

 them out. Those views have obtained their greatest support in the report 

 of Blunck. But since he does not submit the facts upon which his conclu- 

 sions are based it is impossible to know at present whether the larvae that 

 developed in the young stages of Dytiscus were encysted forms that the 

 insect had devoured with prey or whether they were larvae that had 

 merely adhered to the food or had even bored thru the external covering 

 of the insects and thus actively migrated into them. The mere fact that 

 he observed encysted larvae in the prey of the larval beetles would in no 

 way constitute a proof of the fact that these encysted forms were identical 

 with the parasitic stages found later in the beetles. The actual evidence 

 presented up to the present time indicates that there is in the life history 

 of the Gordiacea no encysted stage and no change of hosts. However, 

 different species of the group may differ in this respect. 



Developmental period 



The conclusion of Svdbenik, that the young forms must live several years 

 in the bodies of the insects, is not confirmed by the present report. Blunck 

 also does not indicate that the developmental period is very long, as he 

 states that the parasites usually emerge soon after the beetle has attained 

 its adult form. 



The theory of Villot, Camerano and others that the Gordiacea fre- 

 quently leave their hosts before the cuticula is completely formed has in 

 no way been confirmed in the present work. On the contrary, the obser- 

 vations show that in the species investigated no essential change takes place 

 in the cuticula after the specimens have emerged. The theory was not 

 based upon observations made on the same specimens but merely upon the 

 fact that certain specimens presented slightly different cuticular structures 

 than did others. These differences may have been due to the fact that the 

 specimens developed in different host species or in the same host species 

 under different conditions. The placing of small or light colored specimens 

 in the category of young individuals is based upon no scientifically 

 established facts. The present observations show that the statement of 

 Villot that young specimens of Gordius villoti have a smooth cuticula and 

 that the bristles develop later is founded upon error. Either the smooth 

 individuals belong to a different species from the ones with bristles or the 

 European species is variable in regard to that character. 



ORGANOGENY 



In regard to the organogeny the work of Vejdovsky (1894) stands 

 almost alone. The contributions of Villot on that subject are of little 



