170 Miscellaneous. 



special muscles. These three muscular ribbons start from the base 

 of the styles, and are inserted upon the well-marked constriction 

 which separates the body from the tail. They cause the movements 

 of protraction and retraction of the trunk, which are completely 

 independent of those performed by the rest of the head. The latter 

 are effected by means of the cylindrical subcutaneous muscle, which 

 at the same time gives motion to the circlets of hooks. 



I insist upon this fact, that the first larval form of the 

 Gordius differs greatly from that of the Nematoid worms. In these 

 latter, even including the aberrant genera (Mermis and Sp7icerularia), 

 the embryo and the larva are represented by the type of the Anguil- 

 lulae (Ehabditis). Now it would need a great effort of the imagina- 

 tion to refer the larva of Gordius to this type. The order Gordiacei, 

 as established by Von Siebold, cannot therefore be retained by 

 zoologists, who nowadays attach the greatest importance to the 

 characters furnished by embryogeny and morphogeny. 



The second larval form differs from the first as much as the latter 

 differs from the sexual form. It is characterized essentially by 

 the loss of the styles, the shedding of the hooklets, and the disap- 

 pearance of the annulations. 



Each of the two larval periods includes two very distinct phases, 

 that of parasitism and that of aquatic existence ; but these two 

 phases do not in each case occur in the same order. In its first 

 larval form the young Gordius passes from aquatic life to the state 

 of a parasite ; in its second larval form it quits its post to return to 

 the water. The two phases of parasitism, although immediately 

 succeeding one another, differ essentially. So long as the first 

 phase lasts, the young worm, enclosed in its cyst, remains motion- 

 less and does not appear to take any nourishment or to grow at all. 

 During the second, on the contrary, it is free, lives at the expense 

 of its host, and becomes very rapidly developed. 



It has been supposed hitherto that the passage from the first 

 larval form to the second is connected with a migration, a change 

 of host. The observers who saw larva) of Gordius encyst themselves 

 in larvae of Ephemeridae supposed that the Dytieidae swallowed 

 these encysted larva? with their prey, and that the young Gordii 

 developed themselves in the visceral cavity of their new host. For 

 this hypothesis, which is still classical, I substituted another which 

 appeared to me of more general application. I said that the Gordii 

 parasitic upon fishes proceed from larvae previously encysted in vari- 

 ous species of Tipulidae, the larvae of which likewise lived in the 

 water ; and I founded my argument upon the consideration that 

 fishes are, in general, very fond of those insects. Both hypotheses 

 are contradicted by the well-ascertained fact that the two larval 

 forms of the Gordii live indifferently in the various aquatic hosts 

 indicated. I therefore now regard it as very probable that the two 

 phases of the parasitism of the Gordii are accomplished in one and 

 the same host. 



Observation also proves that the larvae of the Gordii do not select 

 their host. They encyst themselves and become developed in the 

 most different animals (Batrachians, fishes, Crustaceans, Arachnids, 



