the Origin of Intestinal Worms, 398 



nearly as possible. The interest of physiology is often more 

 in the inquiries than in the results; and no inquiry in nature is 

 useless, even though the desired end be sought in vain. These 

 remarks are applicable to the inquiry concerning the exist- 

 ence of equivocal generation in general, and particularly re- 

 garding intestinal worms, as they necessarily lead to the most 

 interesting and important mysteries of nature. 



Sect. 5. Must be subjected to very severe Hestrictions. — The 

 infusory animalcules form distinct species, they have a very 

 complete organization, they multiply in a manner analogous 

 to other animals, partly by eggs, partly by voluntary division. 

 Hence their spontaneous origin, if adopted at all, must be sub- 

 jected to the following restrictions : 1. That their formation, 

 although arising spontaneously, is limited to certain external 

 and internal forms, no intermediate form being permitted. 

 2. That such forms arising spontaneously may have a highly 

 complicated structure, with a harmony as perfect as that which 

 characterizes organisms in general. 3. That these diminutive 

 organisms, themselves spontaneously produced, and the off- 

 spring of no other similar organism, must still propagate them- 

 selves in a manner analogous to other animals. 



With these restrictions, the theory of equivocal genera- 

 tion appears to many physiologists to be deprived of all foun- 

 dation. But it will require little pains to shew, that these 

 same restrictions have long been made in the theory, as ap- 

 plied to intestinal worms. 



As to the first point, it is certain that, in the human body 

 for instance, one Ascaris lumbricoides is invariably precisely 

 like another of the same sex, in respect both to external shape 

 and internal structure. This result is much more easily ascer- 

 tained in these worms than in the infusoria, on account of their 

 greater size. 



As to the complicated structure, it may now be regarded as 

 decided, that it is as perfect in iiitestinal worms in general as 

 in animals of other classes. For the Nematoidea this has 

 been shewn in several species, especially in the Ascaris lum- 

 bricoides. In proof of this, I need only cite the monography 

 of M. Jules Cloquet, although a more complete account of the 

 class may now be necessary. A genus of this order, which 



