THE ACARIXA OR MITES. 



43 



dividing the egg (fig. 60) into lialves and exposing tlie pale vitelline membrane; tliis 

 stage is the "deutovum" of ClaparMe. 



The newly hatched larva is circular or ovoid in outline, with three pairs of legs 

 each tipped with two or three prominent claws. After attaching to the insect the 

 larva becomes elongate and swollen with food. When full fed it drops off. seeks shelter 

 in the soil or under a stone, and remains motionless for sev- 

 eral weeks. The body swells and changes in form as the 

 nymph is developed within ; this stage is called by Henking 

 the nympho-chrysalis. "When ready the nymph issues from 

 the cracked skin of the larva, and after feeding and growing, 

 again resumes a state of repose; this stage preceding the 

 adult condition is known as the teleio-chrysalis; from this 

 comes the adult mite. 



The mature mite is not parasitic, but wanders about feed- ^ j' if 

 ing on small insects, as plant lice, young caterpillars, and ^ f ? 



one species, T. locustarum Riley, is known to destroy a great 

 many grasshopper eggs. A French species has been found 

 destroying the root forms of the dreaded Phylloxera. The 

 adult hibernates in sheltered pMces or in the soil; the eggs 

 are laid in the spring, and there appears to be but one brood 

 a year. Only a few forms have been bred ; the larva of one 

 of them is common on the house fiy in autumn, and a similar 

 form occurs on mosquitoes. 



The old genus Tromhidium has been divided into many genera 

 and subgenera, mostly by Berlese. The characters used do fig. 66.— Larva of Allo- 

 not refer to the appearance of the mite and are often difficult thrombium and mouth 

 to tabulate; the genera that may merit separation are given in parts. (Original.) 

 the following table: 



1. Xo crista metopica Tromhella. 



Crista metopica present 2 



2. Sides of body with projections Chyzeria. 



Body without projections 3 



3. Claws with a puhdJlus ; eyes pedunculate ; one claw at tip of palpus. .Allothrombium. 

 No piil\'illi 4 



4. No eyes 5 



Eyes present 6 



5. Crista enlarged near middle Typhlothromhiiim. 



Crista enlarged at end Trombicula. 



6. Eyes sessile ; palpus with two claws at the tip 7 



Eyes pedunculate 10 



7. Crista enlarged but once 8 



Crista enlarged tvrice 9 



8. Enlarged only at end; aljdomen higher than the cephalothorax. . Mkrotromhidium. 

 Enlarged only near middle; abdomen and cephalothorax of same height. 



Tanawpodus. 



9. Crista enlarged at middle and at end Eutromhidiuin. 



Crista enlarged twicQ near the middle Diplothrombium. 



10. Crista enlarged near middle 11 



Crista enlarged near end 12 



11. Eyes long pedunculate; no teeth at base of the palpal claw Dinothromhinm. 



Eyes short pedunculate; teeth at the base of the palpal claw Podothrombium. 



12. Crista enlarged near anterior end; eyes long pedunculate; no teeth near 



palpal claw ; legs rather short Trombidium . 



Crista enlarged near posterior end; eyes short pedunculate; teeth near pal- 

 pal claw ; legs very long Johnstoniana. 



Oiu* forms have been described under the name Trombidium, and. while their repar- 

 tition into the new generic segregates has not as yet been attempted, it is probable 

 that we have representatives of most of these new genera. Berlese has recently pub- 

 lished a revision of the family, but he had very few species from our countrj% several 



