SCOTTISH HAIRWORMS 113 



infected insect, let us assume, falls a prey to a carnivorous 

 beetle, such as Carabus or Ptcrostichiis^ and along with the 

 young Hairworm imbedded in its bod)', is swallowed. 

 At this point the larval stage of the Hairworm ends and 

 the juvenile begins. The body elongates until it all but 

 fills the abdomen of the beetle, whence, after a period of 

 development which has lasted a year and a half, it issues, a 

 free and almost mature individual. It immediately seeks 

 the nearest water, there finally to lay its eggs.^ In the adult 

 stage the Hairworm endures an enforced fast, for its 

 alimentary tract is degenerate, its oesophagus is blocked by 

 a solid mass of cells, and its tiny mouth is closed by a plug 

 of cuticle. 



I have stated here in dogmatic form a possible and 

 perhaps the normal mode of development of a Hairworm. 

 But it is certainly no hard-and-fast process, for the armed 

 larval stages of various species are found not only in midge 

 larvae such as CJiironomus and Tanypus, and in the larvit of 

 other insects such as alder-flies (Sia//s), mayflies {EpJievierd)^ 

 and water-beetles {Hydrophtlus piceus), but in such odd hosts 

 as a leech {Nephelis), in the foot of pond-snails {Limncea and 

 P/ajiorbis), in the intestinal mucous membrane of the lam- 

 prey, the loach, the minnow, and even of the common 

 frog. It seems likely, however, that the occurrence in these 

 odd hosts is purely accidental, and that in such cases the 

 larvae must die without reaching subsequent stages of 

 development. The juvenile stage also occurs in many an 

 animal outside its normal cycle. Insects may be taken as 

 the usual hosts, and amongst these the Hairworm appears 

 to be restricted to beetles and Orthoptera, many different 

 species of which, carnivorous but not necessarily aquatic, have 

 been victimised. But apart from insects, gordian worms 

 have been found in spiders, in centipedes, in an amphibian 

 {Auiblystomd), in a bird {Otis), in a sheep, and on several 

 occasions in man. It is probable, of course, that in some of 

 these cases at any rate the Hairworm has not undergone 



' Some notes on the seasonal activity of the adult stage, from recent 

 observations made by Mr Wm. Evans, will be found in the account of 

 the Mottled Hairworm, Gordiiis villoH, in the pages which follow. 

 41 P 



