OE LIPE-HISOET OT CERTAIN ACAEINA. 389 



I believe that it will be found that this is not a single species, 

 but is rather the type o£ a considerable genus. I have found 

 a number of females closely resembling those of D. homhi, but so 

 very much smaller that they can scarcely be the same, as inter- 

 mediate sizes do not occur. I have also found in moss a very 

 small species which appears to have the adult female, male, and 

 larva, which is dragged about by the male, all having a sufficient 

 similarity to D. iomhi to justify their being included in the same 

 genus. The adults are usually of a bright green colour, somewhat 

 varied occasionally with yellow and black, the colour being greatly 

 communicated by the food. I hope to describe this more fully 

 on a future occasion, and in the meantime would call it pro- 

 visionally Disparipes viridis. I have also found other creatures 

 which will, I think, have to be allotted to the same genus. 



To summarize the results of my observations, it appears to 

 me : — 



1. That true Hypopi are not adult animals, but are a stage in 

 a life-history. 



2. That they are heteroraorphous nymphs of Tyroglyphus and 

 some allied genera. 



3. That it is not all individuals that become Hypopi, but only 

 a few. 



4. That the hypopial period takes the place of that between 

 two ecdyses in the ordinary life-history. 



5. That, in those species which I have examined, the hypopial 

 stage commences with the second nymphal ecdysis. 



6. That the change to Sypopus is not caused by unfavourable 

 circumstances, and is not any extraordinary or exceptional cir- 

 cumstance, but is a provision of nature for the distribution of 

 the species occurring irrespective of adverse conditions. 



7. That, in the present state of our knowledge, we can no more 

 say why one nymph becomes a Hypopus and another does not, 

 than we can say why one ovum produces a male and anothei* a 

 female. 



8. That Hypopi are not truly parasitic, but only attach them- 

 selves to insects, &c., for the sake of conveyance, and that they 

 do not confine themselves to any particular insect, but adhere to 

 any suitable moving object. 



nous hood covering the front part of the body of the female, and other things 

 would, I think, prevent both species being properly included in one genus. I 

 think Berlese was in error in considering Pygme'phorus to be an immature form. 



