DEVELOPMENT AND IMMATURE STAGES. 155 



parasitic upon Invertebrata.* It contains a summary 

 of existing writings on the subject, but does not record 

 any observations of his own. Still he makes a sugges- 

 tion in it that the hypopial form is a " travelling dress " 

 for Ti/roglyphus, to enable it to endure the journey from 

 one fungus, etc., to another, which would sooner or 

 later become necessary from the drying or destruction 

 of the first fungus. This really is the nearest to the 

 truth that anyone had attained to. 



The above are the principal records, but Mr. J. S. 

 Macintyre informed me that he also had seen Tyroglyphi 

 turn into Hypopi. I am not aware that he published 

 his observations. 



Thus it will be seen that in 1884, when I published 

 the results of my own observations,! there were eight 

 different theories before the world as to what a Hypopus 

 really was, viz. : 



1. H is a separate fiunily of adult f 



' ( some later authors. 



2. Hypopus is an immature stage of Gamasus Dnjardin. 



3. Hypopus is an itch-mite . . . Gerlach. 



4. Hypopus is the adult of both sexes of ") p 



some species of Tyroglyphus . . ) u 



5. Hypopus is the male of Tyroglyphus . Claparede. 



6. Hypopus is the cuirassed, heteromor-,. 



phous, adventitious nymph of Tyro- ) 



glyphus, etc., appearing only for the > Megnin, Berlese, etc. 



preservation and distribution of the i 



species under adverse circumstances .^ 



7. Hypopus is a parasite, at first internal, ") 



afterwards external, which devours its > Andrew Murray. 

 host from within, leaving only the skin} 



8. Hypopus is a travelling dress . . Haller. 



Of these Megnin' s was the generally received theory, 

 and was evidently an approach to the truth. I, how- 

 ever, could scarcely think that it was altogether correct ; 

 and finding the subject interesting I endeavoured to 

 investigate it. 



* ' Die Milben als Parasiten der Wirbellosen, insbesondere der 

 Arthropoden,' Halle, 1880, p. 17. 



f Michael, " The Hypopus Question, or the Life-history of certain 

 Acarina," in ' J. Linn. Soc.,' vol. xvii (1884), pp. 371 394, pi. xv. 



