EVERTEBRATA 483 



completely developed Mermes can become mature whilst still in 

 the soil ; but the normal condition requires the wandering to 

 commence, as we have said, at or near the full time of embryonal 

 development. The embryos are reproduced viviparously, and 

 being set free, they pass a certain period of their existence in 

 the soil. Here they grow rapidly, acquire sexual organs, and 

 subsequently seek to " gratify their immigrative propensities," 

 as Yon Siebold says, by selecting and penetrating the soft-bodied 

 larvae of lepidopterous and other insects. This entrance they 

 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. Yan Beneden thinks it probable that the males 

 quit the host some time before the females, a view which, if 

 correct, might alone account for the comparative scarcity of the 

 males. According to Yon Siebold, sexual congress occurs before 

 the entrance of the worm into the caterpillar. This observation 

 agrees with the generally admitted fact that hitherto no male 

 Mermes have actually been detected in the bodies of insects. 

 The Gordii, like Mermes, become free in damp earth and 

 penetrate the bodies of certain insects or their larvae. Some 

 of them gain access to fishes. Like the free nematodes 

 (Anguillulidtf) , many of the Gordii will survive complete desic- 

 cation. The eggs of the mature worms are deposited in long 

 agglutinated chains in water or damp situations. 



I must conclude. In the body of this work will be found 

 many notices of insect parasites that are awaiting transference 

 to some vertebrate. I need only allude to the r61e of the 

 mosquito, to that of the louse of the dog, and especially to that 

 of the little myriapod (Glomeris) which, like the common 

 glow-worm (Lampyris), possesses phosphorescent properties. I 

 mention this again partly in correction of an entomological 

 error (at p. 296) which escaped me at the time of going to 

 press. Leidy has described a mature nematode (Ascaris infecta) 

 from Passalus cornutus, and numerous Filariae are known to 

 infest insects (Blatta, Forficula, Pliosphuga, &c., &c.). From 

 an earwig I obtained a filaria nearly five inches in length. 



We have seen that the larvae of Dracunculus, CucuUanus, as 

 well as those of other important nematodes, dwell in bodies of 

 entomostracous Crustacea, whilst those of Echinorhynchus attack 



