238 The Zoologist— June, 1866. 



developed, apparently very powerful, and move in a horizontal direc- 

 tion; the two when spread out forming a complete semicircle. The 

 free extremities of the falces are somewhat complicated in structure; 

 on the outside edge is a strong claw, with two short spurs at its base, 

 and immediately within this or the inner side are two combs, very 

 similar in general appearance to the pectinated claws at the extremities 

 of some spiders' feet ; the inner one is smaller than the other, but the 

 two move simultaneously and independently of the outer claw. There 

 are also a few strong hairs situated near the combs. 



When this Acarus seizes another one of a different species, which it 

 does by its falces, laying hold of a leg or any other part indiscrimi- 

 nately, the prey, after a lapse of about fifteen or twenty seconds, 

 becomes poisoned or paralysed, the legs bend up under the thorax, 

 and no part of its body makes any resistance to the pulling backwards 

 of the devourer, who, when she finds this passive condition of her 

 prey, deliberately sucks out the fluids with an apparatus at the mouth, 

 and does not leave it until it is entirely empty and shrunken. The 

 poisoning process, however, does not occur when this Acarus feeds, as 

 it frequently does, upon one of its own species. In this case the prey 

 continues to move and show signs of life as long as any fluids appear to 

 be left in its body, and even, when a very small one has been devoured, 

 I have noticed a movement of the legs full half an hour from the time 

 of its first seizure. 



The parts of the mouth project from the bases of the falces and two 

 sharp pointed and close fitting lancets, answer the double purpose of 

 piercing and conveying the fluids, which appear to be sucked up by 

 a muscular movement at the base of the piercers. The Acarus is suffi- 

 ciently transparent for the process to be watched under the microscope, 

 and the fluids may be distinctly traced in their passage from one 

 acarus to the other. 



The external structure of this Acarus appears to be very simple, and 

 there are but few features to notice beside those of the head. Two 

 rows of short hairs, about twenty in all, run in parallel lines, and a 

 short distance apart, leaving a broad central band, underneath which a 

 large vessel is easily detected, and appears more or less filled with white 

 flocculent matter. In no part can I detect any spiracles or tracheae. 



Of the legs, the first pair are during life constantly raised and 

 lowered in a vertical direction, and from this peculiar action, combined 

 with their two unusually long terminal hairs, I presume they are 

 employed as feelers. The last joint of each tarsus is furnished at its 



