INVERTEBRATA, CRYPTOGAMIA; MICROSCOPY, ETC. 801 



Organization and Development of the Gordii.* — M. A. Villot 

 insists upon the fact, tliat the first larval form of the Gordius differs 

 greatly from that of the Nematoid worms. In these latter, even 

 including tlie aberrant genera (Mermis and SphcBruIaria) the embryo 

 and the larva are represented by the tyjies of the Anguillulje (RJiab- 

 diiis). Now it would need a great effort of imagination 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 difiers 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 booklets, and the disappearance 

 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 

 \vorm, enclosed in its cyst, remains motionless, 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 exj)enso of its host, and becomes 

 very rapidly dcveloiied. 



It lias been sujiposcd 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 larvse of Gordius encyst tliemselvcs in 

 larvaj of Ei^hemeridfe supposed that the Dyticidfe swallowed these 

 encysted larvae 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, the author substituted another 

 which appeared of more general ajiplication. He said that the 

 Gordii parasitic upon fishes proceed from larva; previously encysted in 

 various species of Tipulida?, the larvae of which likewise lived in the 

 water; and he founded Ins argument upon the consideration that 

 fishes arc in general very fond of those insects. Both hypotheses 

 arc contradicted by the well-ascertained fact that the two larval forms 

 of the Gordii live indifferently in the various aquatic hosts indicated. 

 He therefore now regards 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 larva) of the Gordii do not select 

 their host. They encyst themselves and become developed in the 

 most different animals (Batracliians, fishes. Crustaceans, Arachnids, 

 insects, and molluscs). It is therefore by no means the case, whatever 

 may have been said, that the larva) of the Gordii are parasites j^cctdiar 

 to insects. As regards fishes, these are perhaps the animals which 

 harbour these larvro most frequently and in the greatest number. 



♦ 'ComptcH Rcndus,' xci. (1880) p. 15G9. See 'Ann. and Mng. Nnt. Hist.,' 

 vi. (lS80)p. 1G9. 



VOL. III. 3 G 



