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THE POPULAR SCIENCE MONTHLY. 



to have poisoning powers similar to those of the spider. They seize 

 their victim by the leg or any other part, who, after the lapse of 

 fifteen or twenty seconds, becomes paralyzed, makes no resistance to 

 the devourer, and remains passive till nothing is left but an empty 

 and shrunken shell. The poison has no effect on its own species : they 

 frequently feed on each other; but in that case the prey struggles so 

 long as any fluid seems to be left in the body. It is found in the dust 

 of hay, old grain, meal, and flour, on collections, and also on books, 

 from which latter it derives its name ; but, in the opinion of Mr. Mur- 

 ray, it is so found because other gregarious acari congregate there, 

 and " we should no more think that it was there for the purpose of 

 feeding on those stuff's in which it is found than we should admit that 

 a cat eats hay because it is found in a rat-infested hay-stack," 



The occurrence of the phenomena of parthenogenesis among aca- 

 rids has been shown by this species. Mr. Beck succeeded in rearing 

 three successive generations from a female without any intervention 

 of the male. The female is very careful of her eggs : she lays them in 

 a heap, and rests brooding over them, guarding them from attack. 



The itch-mites, Sarcoptes, infest the larger mammals. The com- 

 monest species, S. scabiei, which preys on man, when seen with the 

 naked eye, looks like a. white, shining globe, or a little bladder of 



Fig. 9. 



Sarcoptes scabizi— Male. 



Sarcoptes scabiei— Female. 



water, -^ of an inch long and yi-g- of an inch wide. The microscope 

 brings to view (Fig. 9) a round, flat body, with a head not unlike that 

 of a tortoise, provided with powerful jaws and nipj^ers, tlie structure 

 of which is well adapted to mining the skin. The body is set with 



