DEVELOPMENT AND IMMATURE STAGES. 173 



collects in the cavity of the " thorax " in the form of a 

 spherical mass surrounded by a chitinous envelope ; 

 and thus forms a cyst very similar to those formed by 

 some infusoria previous to the drying up of the water 

 in which they are contained. Megnin suggests that in 

 this condition the nymphal skins containing the cysts 

 would be blown about by the wind, and would thus 

 finally arrive at some place where the conditions would 

 be favourable and would then emerge, and that thus 

 the species would be distributed. 



Megnin says that his species were G. spinipes and 

 G. cursor, which latter is considered a synonym of G. 

 domesticus, but he does not distinguish between the 

 life -histories of the two, nor identify any particular 

 observations with either species. 



I have mentioned below (p. 181) that Megnin' s theory 

 of the entire liquefication of the internal organs of 

 Acari before each ecdysis is not now generally con- 

 sidered correct. The difference of the form which he 

 describes from what I found may possibly arise from 

 his examining his creatures more shortly after the 

 change commenced than I did, or from his G. cursor 

 not really being G. domesticus. 



It is not improbable that Megnin' s idea that the 

 nymphal skin containing his cyst would be blown about 

 by the wind may be correct. I do not see that it 

 would be more liable to be so during this than during 

 any other ecdysis, except that this might last longer ; 

 but undoubtedly the creature protected by the case 

 would bear more exposure than the species during 

 other ecdyses. 



I am not aware that any hypopial stage, either 

 rudimentary or otherwise, has yet been traced in such 

 species as Glycypliagus palmifer, G. plumiger, G. 

 Canestrinii, etc. 



