62 BRITISH TYROGLYPHIM). 



peduncle springs from the side, not the end, of the 

 tarsus (PI. I, figs. 4 6). In this case the action of the 

 claw appears to be rather that of a feeling and search- 

 ing organ than of a holding or walking ^one ; the 

 climbing organ is the tarsus itself, the whole of which 

 is transformed into a great claw-like piece, with a 

 bluntly pointed distal end. 



The caroncle, or sucker, is entirely absent in Rhizo- 

 glyphus and Histio^toma^ and almost absent in Tyro- 

 glyphus, Hericia, etc. On the other hand, it is the 

 principal ambulacrum in Glycyphagus, Chortogly- 

 phus 9 Carpoglyphm, etc. It is a thin membrane, 

 varying in form in different species, and which usually 

 collapses when the tarsus is lifted, its true shape being 

 only visible when it is pressed to the substance the 

 creature is walking on. Almost the only way to see it 

 properly is to put the creature alive into a glass cell 

 and get it to walk on the under- side of the thin glass 

 cover, and examine the caroncle with a microscope 

 while it is doing so. Probably the finest caroncle 

 known to me in the Tyroglyphidse is that of Glycyphagus 

 sciurinus (PL XVIII, fig. 8). 



In the hypopial stage some species, e. g. Hixtiostoma 

 rostro-serratum and H. pulcrum, have the fourth leg 

 terminated by a hair or hairs only, without either claw 

 or caroncle ; this may be the condition of the third leg 

 also, as in Glycyphagus Crameri. 



The Sternum and Epimera, which are such a well- 

 marked feature of the Tyroglyphidge, Sarcoptida3, etc., 

 are chitinized in-pushings of the ventral cuticle, which 

 have formed blades usually exposing their lower 

 edges only on the ventral surface ; the rest of the 

 blade being sunk in the body, and forming a series of 

 rigid skeletal pieces, the sides of which afford surfaces 

 for the attachment of the numerous muscles which 

 arise therefrom. The sternum is a straight blade in 

 the median line of the cephalothorax ; it usually 

 bifurcates at its anterior end like the letter Y, only that 

 the arms are curved, convex on the inner side ; they 



