DEVELOPMENT AND IMMATURE STAGES. 165 



the bodies of ants are apt to do so in very definite 

 positions. A still stranger instance is recorded by 

 Janet with reference to a widely different group of 

 Acarina, viz. the Gramasidae ;* he found that Antertno- 

 phorus Uhlmanni and Cilliba (Discopoma) comata when 

 found upon Lasius inixtus arranged themselves either 

 bi-symmetrically or in the median line ; so as not to 

 upset the balance of the host that carried them. The 

 Antennophorus have their anterior ends directed for- 

 ward when they are on, or rather under, the head of 

 the ant, and backward when on its abdomen. 



The Homopus type of Hypopi are adapted to clinging 

 tenaciously to the hairs of hairy mammals, on which 

 alone they are found. The apparatus by which this is 

 effected is curious ; it varies in detail in different 

 species, but the principle is always the same ; it is as 

 follows : There is not any sucker-plate on the ventral 

 surface as in the ordinary type of Hypopus, so that 

 those of the Homopial type cannot adhere to polished 

 surfaces ; but instead of the sucker-plate, and in about 

 the same position, there is a short longitudinal furrow 

 in the ventral plate commencing at the posterior end 

 of the abdomen and running forward ; in this furrow 

 a hair of the host can lie. Below the furrow are one 

 or two minute chitinous plates, the lower (outer) surface 

 of which is slightly rough, generally made so by more 

 or less regular, parallel, or radiating ridges. From 

 each lower lateral edge of the furrow, and thus on the 

 level of the ventral plate, arises a broad, chitinous lip or 

 wing-like piece, so broad that the two usually slightly 

 overlap in the median line of the body when at rest ; 

 they are slightly flexible, and can be raised or depressed 

 to a limited extent ; probably not by special muscles of 

 their own, but by those which serve to contract or 

 expand the abdomen in a transverse direction. Each 

 lip bears on its upper (inner) surface a rough band 

 which presses upon the hair to be held, and forces it 



* 'Etudes sur les Fourmis, les Guepes, et les Abeilles;' Note 13, 

 sur le Lasius mixtus, I' Antennophorus Uhlmanni, etc., Limoges, 1897. 



