Notes on Tijroghjphidse. By A. D. Michael. 23 



Hypojous, thus found, was neither more nor less than the " parasite 

 of an Orihata " of Canestrini and Fanzago, precisely as the Italian 

 professors had drawn it, with the two great eyes or eye-like organs 

 quite as conspicuous as in their figure. 



With regard to these organs I use the expression " eyes or eye- 

 like organs," because one is rather dubious in pronouncing con- 

 fidently on their optic nature when eyes have not hitherto been 

 found in other Hypopi or other Tyroglyphi, and it would not have 

 been thought probable that the species which developed them would 

 be one which passed the greater part of its existence as a boring 

 creature ; although it may properly be replied that the stage during 

 which the organs are present is one when its boring habits are 

 suspended, and when eyes might be of service to it. The position 

 of the organs would be rather unusual amongst Acarina, being 

 actually on the anterior margin, instead of the dorsal surface, of 

 the cephalothorax ; on the other hand, the position is suitable, and 

 the organs are fairly well protected by a projection of the dorsal 

 chitin which half covers them. The organs have the appearance 

 of large simple lenses, such as we are familiar with in HydracJi- 

 nidse, &c., backed by a very black pigment-layer. To feel 

 confidence, however, in their reaUy being eyes we should trace an 

 optic nerve to them, a process which I fancy would present no 

 slight difl&culty, but I incline to regard them as such. 



A moment's reflection will suffice to show any one acquainted 

 with the group that it is extremely likely that this Hypopus would 

 be found sometimes temporarily parasitic upon Oribatidse as its 

 original discoverers say. The Oribatidse are vegetable feeders 

 and are constantly found under bark, the very places where this 

 TijroglypTius lives. The Hypopus is provided with an efficient 

 sucker-plate, and, like other Hypopi, its habit doubtless is to 

 attach itself by these suckers to small moving creatures, larger 

 than itself, for the sake, probably, of conveyance; and thus it 

 would get carried to new and suitable feeding-grounds. It is 

 scarcely likely, however, that its attentions are solely confined to 

 Oribatidse : it is probable that they are much more widely dis- 

 tributed. 



The discovery of this Sypopus enabled me to investigate 

 further a question in which I have taken an interest for some 

 years, viz. the question of what a Hypopus is, and the causes of 

 its becoming a Hypopus. 



I wiU remind my readers that difierent writers have expressed 

 the following views : — 



1. Hypopus is a separate family of adult Acarina. 



2. Hypopus is an immature stage of Gamasus. 



3. Hypopus is the adult of both sexes of some species of 

 Tyroghjphus. 



