386 ON THE ORIGIN OF ENTOZOA 



he drew forth the worm, a foot and a half in length. Pallas 

 does not tell us whether the worm was living or not; but as the 

 worm diners essentially from the Filaria medinensis, or 

 Guinea worm, which may exist in the body for months and 

 years without exciting suspicion of its presence, it is not to be 

 wondered at that the Gordius, uneasy in its new habitation, 

 should speedily excite inflammation ; and it is said, indeed, 

 that the Gordius is fatal to fish as soon as they become in- 

 habitants of their bodies, and yet fish are infested by their own 

 peculiar parasites without fatal consequences. Bacounim 

 observed, that the Gordius aquaticus (aquarum Taurinen- 

 sium) was destroyed when exposed to a temperature at or 

 above 25° or 26° Reaumur, (90° or 91° Fahrenheit,) in milk or 

 water ; and he asserts, as the result of experiment, that dogs 

 may swallow them with impunity. The Gordius very rarely 

 finds an entrance into man or any other animal, excepting fish; 

 and Pallas, who has seen them nowhere so abundant as near 

 Waldai, says, that in this situation he had never heard of their 

 having been detected under the human skin. Even allowing 

 that the fact of the Gordius taking up its abode in the horse 

 is supported on numerous authorities, it still remains a ques- 

 tion whether the observers have not mistaken the Filaria papil- 

 lose/, equi for the Gordius. A similar error has prevailed in 

 respect to nearly all the Ascarides offish, — for they have been 

 mistaken for Gordii ; and I have observed, in dissecting dead 

 fish, Ascarides which have left their usual situation, and wan- 

 dered into the mouth and branchiae. Degeer (in Bibl. n. 234) 

 describes a certain species of Filaria infesting a kind of moth, 

 and in another place a plate is given of it, when it stands for the 

 true Gordius aquaticus. The doctrine of the metamorphosis 

 of worms was long since refuted by Vallisnieri, and I shall 

 briefly notice that such a metamorphosis does not take place 

 in any of these animals, neither amongst the viviparous or 

 oviparous, for the same gradual evolution and perfection of the 

 body which is observed in all the other classes of animals is 

 necessary here. 



" A cow to bear a fawn you ne'er did see, 

 Nor eagle's egg the gentle dove set free." 



There are certain peculiarities which distinguish fcetal and 

 adult Entozoa, but in these no perceptible change whatever 



