goediidj:. 



61 



by boring its way out of tlie body of the host. Some discrepancy 

 of opinion exists as to the actual condition of the parent at the 

 time of its wandering, for Von Siebold asserted, that it quitted its 

 parasitical mode of life " in order to become sexually mature away 

 from the animal" infested ; whereas. Van Beneden states, that the 

 embryos are always formed at the time of the wandering. From 

 Siebold' s interesting experiments it would appear that incom- 

 pletely developed Mermes, accidentally or otherwise separated from 

 their hosts, and placed in moist earth, are capable of becoming 

 sexually mature, whilst still in the soil ; but in all probability the 

 normal condition requires the wandering to commence, as before 

 remarked, at or near the time of full embryonic development. In 

 any case the embryos are viviparously reproduced, and being set 

 free they pass a certahi time of their early life in the earth. 

 Here they grow rapidly, and acquire sexual organs, subsequently 

 seeking, as Von Siebold happily expresses it, to "gratify their 

 immigrative propensities," by selecting and penetrating into the 

 soft-bodied larv^ of lepidopterous and other insects. This entrance 

 they are enabled to accomplish by means of a sharply-pointed dentule 

 or boring stylet, which at the time of disuse is concealed within 

 the head. Having once gained access to the host they remain 

 within its body until the caterpillar has become transformed into 

 the perfect butterfly, or until their own sexual maturity is completed. 

 Van Beneden thinks it probable that the males quit the host some 

 time before the females, a view which, if correct, sufficiently ac- 

 counts for the comparative scarcity of the males. According, 

 however, to the experimental records of Von Siebold sexual con- 

 gress occurs before the entrance of the worms into the caterpillars, 

 an observation, which, if established, would render the entrance 

 of male Mermes into the body of the insect host quite unnecessary 

 — that is to say, of no necessity as regards the sexual function. In 

 my opinion this is actually the case with Dracunculus, and explains 

 how it happens that no male Guinea-worms have yet been dis- 

 covered within the human host. So far as I am aware, the presence 



