292 



ARACHNOIDEA, 



CASE to reconcile it with the general accuracy of Furstenberg's repre- 

 sentations. He thinks he may have been misled by having made 

 his observation by crushing some individual that was about to 

 cast its skin, so that he saw both the mandibles in the old skin 

 and in the new ; and, having once detennined the fact, of course 

 it would not be necessary that he should trace it in every indi- 

 vidual or species that he figured of the genus. In all, young and 

 old, and of every species, he certainly represents the four nippers 

 as present. The light in which we felt disposed to regard them 

 was, that although all four are alike, one pair represents the 

 mandibles and the other the maxillae, of which there is no other 

 trace. On the other hand, in both the genera, Symbiotes and 

 Psoroptes, Furstenberg figures only one pair of mandibles as 

 present (chelate in the one and divided in the other), and no 

 trace of maxillae; consequently we think it best to reserve our 

 judgment, merely noting the point as one deserving the examina- 

 tion of some of our good microscopists. 



Nos. Sarcoptes scabiei {Latr.). — 1. Two eggs of ditto, one closed and one 

 1, 2, 3, 4. opened, to show the embryo within, ready to be hatched ; 2. Magnified 



diagram of the bun-ow in the human skin, with the insect at the further 

 end, and the gallery encumbered with eggs and broken egg shells, 

 debris, &c. ; 3. Magnified sketch of male— upper side ; 4. Magnified 

 sketch of female— under side. Copied from figures by Furstenberg. 



Sarcoptes scabiei, male. The itch mite. 



Ditto female. Reduced from Furstenberg 



