the Origin of Intestinal Worms, 325 



instance, in the numerous forms of carbonate of lime, a funda- 

 mental form is still observed to prevail, whereby this variety is 

 limited. In confirmation of this view, we may adduce the obser- 

 vations which have been made upon hybrid animals^ which can 

 scarcely ever procreate, as if nature were averse to hybrid forms 

 in general. Finally, the defenders of equivocal generation pre- 

 tend that new forms will arise in every case where altogether 

 new conditions exist, as has been stated with regard to algas 

 and other such plants ; but it is quite as difficult to prove these 

 views, as it would be to refute them. 



Sect. 2. But makes it very doubtful, — Thus the first-named 

 restriction to the doctrine of spontaneous generation, although 

 it contains no decided proof against the theory, should make us 

 hesitate much before we adopt it. For, as it is safer to trust 

 little to our own sagacity, and much to the expedients of nature, 

 it seems wiser, on discovering the same animal here and there 

 and everywhere, to conclude that this animal, by its natural in- 

 stinct, has found means to multiply in some way which escapes 

 our observation, than to maintain that this process could not 

 have eluded us, and that nature must afresh have created new 

 specimens precisely of the same stamp as those all around us. 

 I say all around, for if we consider how extremely minute are 

 the quantities submitted to microscopical examination in the 

 experiments upon infusory animalcules, and how repeatedly 

 the same forms recur, we cannot but acknowledge the com- 

 mon forms of infusoria to be spread wheresover a drop of fluid 

 is to be found. 



Sect. 3. Particularly in respect to the Entozoa^ or Internal 

 Worms. — It was previously observed, that the constancy of forms 

 was much more easy to ascertain in intestinal worms than in the 

 infusoria, on account of their greater size. But it is likewise 

 much more difficult to make this constancy of form harmonize 

 with the supposition of their spontaneous origin. To maintain 

 that the contents of the human intestines are, by a kind of fer- 

 mentation, metamorphosed into living animals which, notwith- 

 standing the immense variety of food in men of diff^erent condi- 

 tions, always prove to be the Ascarides lumbricoides, Taeniaj so- 

 lium, or Bothriocephali lati in the smaller intestines, and the As- 

 carides vermiculares, or Tricocephali dispares in the larger, will 



