432 Bi-V G. Meissner on the Genus Merrais. 



of Siebold we are indebted for the successful solution of the 

 whole enigma, and the results he has obtained are as singular 

 as new*. It appears that these animals live part of their 

 life as regular entozoons, and the rest as independent beings. 

 And what is most remarkable, they enter the animals in which 

 they are for a time parasites, not in the form of eggs, as do 

 other Helminths, but as more or less developed forms. The 

 animals in which they live as parasites are almost exclusively 

 Insects of different orders, in both the larva and imago states. 

 In the abdominal cavity of the larva of Yponomeuta albicans, 

 Siebold found numerous undeveloped forms of Mermis albicans. 

 Watching these he found that after further growth, they per- 

 forated the skin of these larvse and made their escape. These 

 freshly-escaped individuals were all sexless, but each contained 

 a considerable corpus adiposum^ at the expense of which their 

 sexual parts were subsequently developed. These animals 

 crawled about, and soon entered some damp earth, where they 

 remained several months, during which time they were further 

 developed, changed their skin, copulated and laid their eggs. 

 The embryos hatched from these eggs had the filamentoid form 

 of the adults, and as Siebold conjectured that they intended to 

 come to the surface for the sake of entering in their turn young 

 insects, he procured quite young larvse of this same insect and 

 put them in a glass vesael together with the young Mermithes. 

 In a few hours they had entered the body of these larvje, two or 

 three in each. Siebold took the precaution to make this point 

 certain by carefully examining the larva? previously and deter- 

 mining that their bodies were free of these parasites. After 

 this, the same round of life is again passed. It would appear, 

 then, that these animals pass their earlier (but not their 

 embryonic) conditions of life, during which they attain their 

 development — in fact a proper larval state — in the bodies of 

 insects, and that their life as distinct sexual individuals is free 

 and non-parasitic. Siebold found this species in very many 

 genera of Lepidoptera, also in different species of Orthoptera, 

 Coleoptera, and Diptera. We may mention that the common 

 Cricket, as also some other Orthoptera, are frequent recipients of 

 Mermis, and we have seen many specimens of this kind. Until 

 Siebold's recent contributions we had supposed, in common with 

 other naturalists, that these Helminths merely hibernated in 

 these insects, but this is now quite improbable. 



So much for a brief reference to the mode of life of these 



u^'-^* Siebold. See the Entomol. Zeitung zu Stettin, 1848, p. 292, 1850, 

 pf. 329; also Beitrage zur Naturgeschichte der Mermithen, in Siebold und 

 Kolliker's Zeitsch. fur wissensch. Zool. v. 1853, p. 211. 



