1j4 Appendix. 



result of their writings was to entirely subvert the belief in the 

 spontaneous generation of insects and all animals of a higher 

 organization. Since their day no one of any scientific preten- 

 sions has ventured to propound this theory for any species of 

 aniaial life with a high grade of organization.* 



The discovery of the mammalian egg which dates from 1673, 

 by De Graaf, of Delft, in Holland, and the full history of its 

 mode of development which was closed by Von Baer, in 1827, 

 threw a flood of light upon the general question of generation, 

 and stripped it of the mystery which hitherto had been care- 

 lessly supposed to surround it in the highest orders of animals, 

 especially in man himself. Its bearing, too, upon our subject is 

 obvious. In this way " spontaneous generation lost its rank as a 

 great natural division of the reproductive function ; and came to 

 be regarded as an exceptional phenomenon, confined to a very 

 few species whose existence could not be accounted for in the 

 ordinary way. Its territory was narrowed exactly in proportion 

 as the knowledge of natural history advanced ; and it became 

 reduced almost exclusively to the class of animals known as 

 entozoa or internal parasites.'"''* 



These are organisms, some of them microscopic in size, that 

 live within and prey upon the bodies of other animals. They 

 are found in special habitats or organs, and each species of ani- 

 mal has its own particular parasite. Thus, confining our illus- 

 trations to a few only of those met with in the human body, we 

 may notice the different varieties of solid and hollow worms 

 {sterelmintha and ccelehniniha) that infest different portions of 

 the alimentary canal ; the trichina spiralis that dwells in muscle; 



at Padua, and was especially celebraied for his rcheavches into the various 

 systems of generation. His works were published in three volumes folio, at 

 Venice, 1733. 



* Mr. Crosse's electrical spiders {Sequel to Vestiges of Creation), a kind of 

 " microscopic porcupine," which he asserts were developed in a .solution of 

 silicate of potash, through which the consLant galvanic current was continu- 

 ously passed for two years, are unworthy tlie dignity of a serious refutation. 

 A writer in the Edinburgh Magazine, April, 1867, humorously depicts this, and 

 very appropriately too, as a most singular case of delusion. 



** Dalton: loco citato, p. 121 



