31 



of having every advance of knowledge of the operation of 

 such essential condition applied to it. 



When however M. Morren affirms " que la generation se 

 fait ici, comme chez quelques Entozoaires, par Findividuali- 

 sation d'un tissu precedemment organise/ 3 the objection 

 immediately arises, that no one has ever seen a portion of 

 mucous membrane, muscular fibre, or other organized tissue 

 detach and transform itself into an entozoon : such a pro- 

 cess is as gratuitously assumed, and as little in accordance 

 with observed phaenomena, as ( spontaneous generation * in 

 the abstract. In a former Course I objected that " The fis- 

 siparous nucleated cells of the ovum, once metamorphosed 

 into a tissue, can produce nothing higher, and nothing 

 else save by their decay, which products are excreted : but 

 the cells which retain their primitive state amidst the 

 various tissues which the coalescing cells have constituted 

 in building up the body of the new animal may, by virtue 

 of their assimilative and fissiparous forces, lay the founda- 

 tion for a new organism. 5 ' I shall not however here pursue 

 the argument which is carried out in my published e Lec- 

 tures on the Invertebrate Animals/ but shall proceed in 

 the next Lecture to compare the phaenomena of generation 

 from virgin larvae, and the successive production of many 

 individuals from a solitary ovum, which other classes ex- 

 hibit, and to consider the explanations that have been 

 offered of such phaenomena, and how they have been gene- 

 ralized. 



