THREAD-WORMS. 305 



indicate that they must have been precipitated with 

 the rain. I am indebted to Sir Thomas Tancred, of 



racters by which they are distinguished from those genera of 

 worms most nearly allied to them. He has dwelt especially on 

 the tegumentary system, and the reproductive organs, which last 

 have much of peculiarity in respect of the mode in which the 

 eggs are gradually developed. The digestive apparatus is very 

 simple, at least in the adult state ; for the embryo is provided with 

 a distinct intestine. And comparing this embryo, (so similar to 

 the small eel-like worms found in damp earth, and amongst moss, 

 as well as in the visceral cavities of earth-worms, slugs, insects, and 

 their larvae,) with the adult Mermis, in which, by reason of the 

 excessive growth of the tegumentary system and the reproductive 

 organs, the digestive apparatus is become incomplete and in part 

 rudimentary, Dujardin is led to conclude that the Mermis, as 

 already observed, is the last stage of development of an entozoon, 

 different from all the known Nematoidea, undergoing great 

 changes with age, and only arriving at this last stage, in the bodies 

 of \&r\se or insects whose life is sufficiently long. It comes 

 afterwards into the air merely to lay its eggs, and then dies. It 

 is not, therefore, a terrestrial or an aquatic worm, but an intestinal 

 one ; for which, on account of its peculiarities, Dujardin conceives 

 it necessary to create a new order, intermediate between the Nema- 

 toidea: and the Acanthocephali. 



The characters of the genus Mermis are thus laid down : 

 Vermis, corpore longissimo filiformi, elastico, antice paritmper 

 attenuate ; capite subinflato, ore terminali minimo rotunda ; intes- 

 tino simplice, postice obsoleto, ano nullo ; vulva, untied, transversd. 



Ova juxta placentas lineares, intra tubum muscularem concepta, 

 denique in capsulis monospermis, bipolaribus, bipedicellatis, deciduis 

 inclusa. 



The species described by Dujardin, and which there is great 

 reason to believe is identical with the worms noticed in the text, 

 and found at Fairford, he calls Mermis nigrescens. It is thus cha- 

 racterized : Mermis caudd obtusd, capite subarigulato ex papillis 

 5-6-obsoletis ; ovis nigris. 



