DEVELOPMENT AND IMMATURE STAGES. 161 



any small living object that came within its reach, and 

 thus be carried to fresh places suitable for it. Were 

 the adult, the larva, or the ordinary nymph carried by 

 such creatures as flies, bees, etc., which delight in hot 

 sunshine, they would be killed ; the hypopus, however, 

 can endure heat and absence of moisture very much 

 better. Hypopi sometimes remain a long time in that 

 condition ; I have had them over three months. 



I therefore came to the following conclusions, viz. 



1. That Hypopi are not adult, but are an immature 

 stage in a life-history. 



2. That they are heteromorphous nymphs of Tyro- 

 glt/phuH and some allied genera, such as Histiostoma, 

 Rhizoglyphus, Histiogaster, etc. 



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

 usually only a comparatively small number, and that 

 these are of both sexes. 



4. That the hypopial period occupies the time 

 between two ecdyses in those species which I had 

 examined. 



5. That the change to Hypopus is not caused by 

 unfavourable circumstances, and is not any extra- 

 ordinary or exceptional occurrence, but is a provision 

 of nature for the distribution of the species occurring 

 quite irrespective of adverse conditions. 



6. That in the present state of our knowledge we 

 can no more say why one nymph becomes a Hypopus 

 and another does not than why one ovum produces a 

 male and another a female. 



7. That Hypopi are not true parasites, that they do 

 not prey upon the host or obtain any nourishment 

 from it, but only attach themselves to insects and other 

 creatures for the sake of conveyance, and that they do 

 not confine themselves to one species of insect, etc., 

 but adhere to any suitable moving creature. 



8. That the outward form of Hypopus is a protective 

 provision to enable the creatures when in transitu to 

 endure the heat and drought to which they are exposed, 

 which would otherwise kill them. 



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