OF THE MILK. 393 



generation, and the occasionally manifest source of the difficul- 

 ties which obstruct our enquiries, lead necessarily to the belief, 

 not of the unreality of the fact, but of our deficient penetration.* 



The simplest mode of increase is by the detachment and inde- 

 pendent existence of a portion of a system. In this way trees, f 

 polypes, some worms, and many animalcules, X multiply. 



Next comes the formation of the rudiments of a perfectly new 

 being by the system of another. Thus we have the seed of ve- 

 getables, the ova and foetus of animals. This occurs by means 

 of two matters, which in some examples are furnished by the 

 same, and in others, by different, systems. The vegetable king- 

 dom affords innumerable instances of the former, the acephalous 

 mollusca and the echinus are examples in the animal kingdom. § 

 Both the vegetable and animal kingdoms abound in instances of 

 the latter. Here again there are three varieties. The fluid of 

 the male may be applied to the ova of the female after they are 

 discharged from her body, as in fish of the bony kind and in 



* See Cuvier's Anatomie Comparee. — Generation. 



+• Hie plantas tcnero abscidens de corpore matrum 

 Deposuit sulcis ; hie stirpes obruit arvo, 

 Quadrifidasque sudes et acuto robore vallos ; 

 Silvarumque alia? pressos propaginis arcus 

 Exspcctant, et ^ iva sua plantaria terra ; 

 Nil radicis egent aliae ; summumque putator 

 I laud dubitat terrae referens niandare cacumen. 

 Quin et caudicibus seeds (mirabile dictu) 

 Truditur c sicco radix oleagina ligno. 



Virgil. Georgica. Lib. ii. 



X See Spallanzani's admirable Observations et experiences sur les Animalcules. 

 le found a small portion detach itself from the bodies of some, the bodies of 

 •thers split longitudinally, of others transversely, of others both longitudinally 

 nd transversely into four parts, and the new animalcules soon acquired the 

 ize of the parent and experienced the same changes in their turn. 



§ It is singular that some hermaphrodites do not impregnate themselves, but 

 mtually impregnate and are impregnated by others ; such are the gastero- 

 odous mollusca and manv worms. 



