378 OF THE NISUS FORMATIVUS. 



singular experiment of impregnating those which are 

 prolific, for many generations, with male semen of 

 the same species, by means of which the form of the 

 young hybrids becomes so progressively different from 

 the original maternal configuration, as to approach 

 more and more to that of the father, till, by a kind 

 of arbitrary metamorphosis, it is absolutely converted 

 into it.* 



591. Such in our knowledge of monsters (which, 

 according to the hypothesis of evolution, are nearly 

 all maintained to have pre-existed in the germs from 

 the first creation), is the well known fact that among 

 certain domestic species of animals, and especially 

 among sows, monstrosities are very common, whereas 

 in the original wild variety they are extremely un- 

 common. 



592. While the phenomena of reproduction are all 

 much more explicable by the nisus formativus than 

 by the pre-existence of germs for every part, some 

 particular instances (v. c. that of the nails, which, 

 after the loss of the first phalanx of the fingers, 

 have been known to be reproduced on the neighbour- 

 ing middle phalanx, f) admit evidently of no other 

 solution. 



593. From an impartial view of each side of the 

 question, it will clearly appear, that the defenders of 

 the germs must allow to the male semen, not only an 

 exciting power, as they do, but likewise great formative 

 powers, and thus their doctrine stands in need of the 



* Jos. G. Kolreutcr, Drittc Fortsetz. tier vorliiuf. Nachr. j>. 51 sq. 

 t Tulpins, Obscrvat, Med. L. iv. c. 5C. 



