Notes on Mr. Cross's Acarns. 



57 



er, distinctly perceive in it an upper lip, notched at its extre- 

 mity, beneath which a dagger-shaped rostrum projected, and 

 under this, but situated laterally, we found two large move- 

 able mandibles, which were pointed, and slightly bent in- 

 wards. Within these, and pointing in the same direction, 

 were two palpi, shorter than the mandibles, and nearly hidden 

 by them, and the lip which protected them. 



5 



Acarus horridus, Turpin. 



Having had but one individual at our disposal, it has not 

 been possible for us to establish the existence of a lower lip, 

 which is so large and so evident in the Acarus infesting the 

 human body. Neither have we been more fortunate with re- 

 gard to the two small smooth eyes, situated on the neck of 

 the other species of this genus. 



On the circumference of a kind of sternum are placed eight 

 limbs, all locomotive and articulated ; the four anterior direct- 

 ed towards the front, and the four posterior towards the hinder 

 part. They are all composed of the same number of pieces ; but 

 as may be remarked in many insects, and in the Arachnida and 

 Crustacea, the two anterior pairs of limbs are shorter, thicker, 

 and more robust than the hinder ones. This difference, though 

 hardly observable in the Acari of cheese and flour, is very 

 great in the Acarus of the human body ; in which, without 

 an attentive examination, we might be almost led to suppose 

 that the two pair of posterior limbs, which indeed are only 

 rudiments, were organs of a different kind. 



r 2 



