132 BRITISH TYKOGLYrHIM. 



THE LARVA. 



The larva of every species of the Tyroglyphidse, 

 the stage of which is known, is hexapod ; this dis- 

 tinguishes it sharply from the nymph and imago, which 

 are invariably octopod. It is the fourth pair of legs 

 which is absent ; this, as far as is known, is the rule 

 in all Acarina. The larva usually greatly resembles 

 the nymphs and adults, sufficiently so, in most cases, 

 to be recognised ; but there are some characters by 

 which in many cases the larva could be known even 

 if it were not for the hexapod condition. One of the 

 principal of these is the absence of external genital 

 organs, but this it shares with the first nymph, and 

 often with the older nymphs ; as will be seen, however, 

 from the latter part of this chapter, the development 

 of the internal genital organs has commenced even as 

 early as the larva. 



One character which, when present, is specially 

 characteristic of the larva, is what Claparede calls 

 the provisionary " Bruststiele." These are a pair of 

 round rods of clear chitin, placed one on each side of 

 the body just anterior to the epimeron of the second 

 leg; the proximal end of the rod is attached to the 

 ventral surface of the larva by a flexible joint, so that 

 it is capable of motion. The distal end is generally 

 a little knobbed, or clavate, never pointed as far as has 

 been observed hitherto. The function of this organ is 

 entirely unknown ; it has not ever been seen on any 

 nymph or imago : it appears to be always present in 

 larvae of the genus Tyroglyphus, as far as the larvae of 

 that genus have been recorded, and in those of some 

 allied genera, but it is not found in those of Garpo- 

 glyphus and some other genera. 



The larvae of the Tyroglyphidee frequently have 

 only the epimera of the first pair of legs joined to the 

 sternum or to each other ; although in the adults the 

 second pair may also be joined. In some cases the 



