250 ON GENERATION. 



expanded and looks pellucid, the inferior has become more 

 dense, and with the thicker portion of the albumen has sub- 

 sided to the sharp end of the egg. The tunica propria of the 

 upper portion of the yelk is so thin that it gives way on the 

 slightest succussion, when there ensues admixture of the fluids, 

 and, as we have said, interruption to the further progress of 

 the process of generation. 



And now it is that the rudiments of the embryo first become 

 conspicuous, as may be seen in the fifth and sixth figure of 

 Fabricius; the egg being put into fair water it will be easy to 

 perceive what parts of the body are formed, what are still 

 wanting. The embryo now presents itself in the form of a 

 small worm or maggot, such as we encounter on the leaves of 

 trees, in spots of their bark, in fruit, flowers, and elsewhere ; 

 but especially in the apples of the oak, in the centre of which, 

 surrounded with a case, a limpid fluid is contained, which, gra- 

 dually inspissated and congealed, acquires a most delicate out- 

 line, and finally assumes the form of a maggot ; for some time, 

 however, it remains motionless ; but by and by, endowed with 

 motion and sensation it becomes an animal, and subsequently 

 it breaks forth and takes its flight as a fly. 



Aristotle ascribes a similar mode of production to those crea- 

 tures that are spontaneously engendered. 1 " Some are engen- 

 dered of the dew," he says, " which falls upon the leaves/' 

 And by and by he adds, " butterflies are engendered from ca- 

 terpillars, but these, in their turn, spring from green leaves, 

 particularly that species of raphanus which is called cabbage. 

 They are smaller than millet seeds at first, and then they grow 

 into little worms ; next, in the course of three days into cater- 

 pillars ; after which they cease from motion, change their shape, 

 and pass into chrysalides, when they are inclosed in a hard 

 shell; although, if touched, they will still move. The shell 

 after a long time cracks and gives way, and the winged animal, 

 which we call a butterfly, emerges." 



But our doctrine and we shall prove it by and by is, that 

 all animal generation is effected in the same way ; that all ani- 

 mals, even the most perfect, are produced from worms ; a fact 

 which Aristotle himself seems to have noted when he says : 



1 Hist. Anim. lib. v, c. 19. 



