HYPOPIDJE. 231 



CASE Mr. Robertson reports of his species that it is a small maggc. 

 like animal, distinctly visible to the naked eye, and that it was 

 found chiefly amongst the connective tissue of the skin, on the 

 large veins near the heart, and on the surface of the pericardium. 

 When few were observed, these were generally found adhering 

 closely to the large veins near the heart If the veins have been 

 previously injected with size and vermilion, the white transparent 

 acari are seen very distinctly on the red delicate walls. All the 

 examples which he examined were very transparent, without any 

 trace of well-defined digestive or generative organs, even when 

 examined with the highest powers. He adds that he had 

 examined a considerable number of both the wood and tame 

 pigeon and seldom found them free from these or similar Acari. 



Sub-family Hypopid^. 

 The characters of the sub-family are the same as those of the 

 genus, for although it contains two or three different forms, which 

 probably may hereafter be resolvable into separate genera, we 

 have not as yet thought it necessary to introduce these. 



Genus Hypopus {Diigh). 



Until recently the study of this genus was attended with no 

 particular interest beyond that attaching to its fellow mites ; but 

 in 1868, an element of doubt and uncertainty was introduced by 

 M. Claparede, who announced, as the result of his researches 

 ("Studien an Acariden"), that the genus hitherto known as Hy^ 

 popus was only a male form of certain Tyroglyphidae evolved 

 out of the larvce in the same way that we have seen the perfect 

 Iloplophora appear. To enable the reader to understand the 

 position of this curious question, we must give him a short history 

 of the observations on Hypopus. 



In August, 1735, De Geer observed great numbers of very little 

 mites on the house-fly. They were in such large numbers, that 

 the neck and back were entirely covered with them. They were 



