GENERATION OF INSECTS. 411 



With regard to the hypothesis of spontaneous generation, the 

 reasons which have led me to concur with most physiologists of the 

 present day in rejecting it were fully given in a former Course of 

 Lectures on the subject of Generation, and every exact observation 

 and experiment subsequently recorded serve to render that hypo- 

 thesis less tenable and more gratuitous. 



Professor Morren, a comparatively recent and very exact observer 

 of the anatomy and generative economy of the Aphides, retaining 

 the hypothesis of spontaneous generation as it has been applied to 

 the Entozoa, propounded, though not without reserve, a theory that 

 the larval aphides were developed in the body of the virgin parent, 

 like Entozoa, "by the individualisation of a previously organised 

 tissue." Now here also is a phrase which, when the meaning of it 

 is analysed, does little more than express the old facts in a new way. 

 When a larval aphis is developed, a new individual exists ; in other 

 words, it has been "individualised;" and, as nothing can come out 

 of nothing, it must have been by the individualisation of a previously 

 existing something. The question to be solved is, what is that 

 something, and what has happened to that something to make its 

 individualisation under the form of a larval aphis possible and con- 

 ceivable by us according to the known analogies of other embryonic 

 developments or individualisations ? That would be the explana- 

 tion of which we are in quest, — an explanation going as far as that 

 which we are able to give, for example, of the development of an 

 ordinarily impregnated ovum ; and, by the proved analogy of the 

 essential condition of the development in the virgin aphis with 

 that condition in the impregnated ovum, capable 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 I'individualisation d'un tissu 

 precedemment organise *," the objection immediately arises, that no 

 one has ever seen a portion of mucous membrane, muscular fibre, 

 or other organised tissue detach and transform itself into an ento- 

 zoon : such a process is as gratuitously assumed, and as little in ac- 

 cordance with observed phenomena, as " spontaneous generation" in 

 the abstract In a former Course I objected, that "the fissipa- 

 rous 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 



* Annales des Sciences Nat t. v. 1836, p. 90. 



