DERIVATION OF ORGANIC BEINGS. 7 



dently of parents or their spontaneous generation, as it has 

 been called is to be held inadmissible. This is especially 

 the case in regard to the development of parasitic beings ; 

 but so much has been done of late years in the investiga- 

 tion of these obscure cases, as to render it highly probable 

 that those as yet unexplained are no real exception to the 

 general law of parental derivation. The facts which have 

 come to light in the pursuit of such enquiries are of a kind 

 equally surprising and interesting, but it would be out of 

 place to refer to them more in detail here, as many of the 

 phenomena will again come under notice in the farther 

 treatment of the subject proposed for discussion in this 

 work the laws regulating the derivation of living beings 

 from each other. It may suffice, therefore, to close this 

 allusion with the following summary of the subject, in the 

 words of Prof. Owen : "The ' thread-worms ' (Filaria?) of 

 certain insects, which present no trace of sexual organs, 

 were supposed to be spontaneously developed in those in- 

 sects. The little worms were, however, by special and 

 due research seen to wind their way out of the caterpillars 

 they infested. Von Siebold placed these free Filarioe in damp 

 earth, into which they soon bored : in a few weeks he found 

 that the sexual organs were developed in them, and that 

 they laid hundreds of eggs. Early in spring the young 

 worms were hatched, and began to creep about. Von Sie- 

 bold took some young caterpillars of the moth (Iponomeuta 

 ewnymella) in which were no parasites : he placed them in 

 the soft earth in which the young Filarice had been hatched, 

 and, in twenty-four hours, most of the caterpillars were in- 

 fested by the young thread-worms, which had bored their 

 way through the soft skin, into the interior of the young 

 caterpillars. The long hair-worm of fresh waters (Gordius 

 aquations), vulgarly conceived to be the result of a meta- 

 morphosis of the hair of a horses' tail, passes its early life 

 as a parasite in the body of an insect. But many Entozoa 



