IN THE BODIES OF ANIMALS. 387 



takes place ; and if any really does occur, it is so inconsiderable 

 that they may be easily recognised. Some naturalists, indeed, 

 have carefully observed, during many years, the growth of in- 

 testinal worms : nor are we ignorant that insects which take up 

 a temporal abode in the animal body undergo a metamorphosis ; 

 these are furnished with a special apparatus for that end, 

 which may be observed in certain larvae ; but the structure of 

 insects is much more complicated than that of the Entozoa and 

 Gymnodela. Kunsemiiller must certainly have overlooked 

 this, when he pronounces it as a still doubtful question 

 whether the Vena medinensis, or Guinea-worm, be a naked 

 worm, or the larva of an insect which lives in stagnant waters 

 and marshy situations, and deposits its ova under the human 

 skin ; for the larvae of insects differ widely from all the Entozoa, 

 and from the Filarice in particular, even the most simple of 

 them, and this both in external form and internal structure. 

 Jordens is drawn into a somewhat similar error, and he de- 

 scribes, as a new species of Ascarides, two larvae of the genus 

 Musea, dejected by a man, and thus enriched the genus by 

 adding the two species Stephanostotna and Conostoma ! 



Although the advocates of this doctrine may be convinced 

 of its fallacy by these and such like arguments, and may be 

 satisfied of the impossibility of extrinsic worms finding an 

 entrance into the deep-seated parts of the body which are 

 obnoxious to certain species of worms alone, they allow addi- 

 tional latitude to their imagination, and conceive that, instead 

 of the animals themselves, their ovules may be carried into the 

 body. 



Many of the ancients, and some of the moderns, have con- 

 ceived that the ovulae of worms, which pass out of the animal 

 into the air and water, may be carried into the bodies of other 

 animals through the medium of food and drinks, and, being 

 deposited there, become hatched. This idea owes its founda- 

 tion, no doubt, to the observation of a profusion of eggs in the 

 genital apparatus and ovaries of certain worms ; and the expe- 

 I'iment instituted by Pallas, in which ovules placed in the 

 stomach of a dog produced young Tcenice, was considered by 

 him conclusive of the question. This celebrated individual 

 has been much praised for this discovery, but he is obliged 

 to support his position by a variety of arguments, many of 

 which are opposed to the result of his experiments. He thinks 



