THE ACAEIXA OR MITES. 141 



are very minute, rarely over 1 mm. long, and occur in wet moss, such as is found in 

 old gutters, on stones, or old walls; a few live in water; two are known from salt water. 

 Their body is apparently segmented and tipped with a pair of fleshy processes bear- 

 ing apical claws. Other similar processes occur on the sides of the body, also tipped 

 with claws. Those species that inhabit moss possess a most remarkable power of 

 revi\'ification. If they are gradually dried up they may remain so for years, but on 

 the application of water they gradually revive, swell out, and begin to live again. 

 There are about 6 genera, and many species described. In some cases the same 

 species occurs in England and in Chile, at sea level, and up to 11,000 feet. Of the 

 two principal genera, Echiniscus has 

 dorsal shields on the body, and Ma- 

 crobiotus is without shields and with 

 a rather longer body. A number of 

 species have been described from 

 Canada. 



The third group, Pycnogonida (fig. 

 294), or "sea spiders," are slender- 

 bodied, long-legged forms living in 

 salt water. They have some resem- 

 blance to acari, but probably little 

 real relationship. The fact that the 

 best-known species had four pairs of 

 legs suggested their association with 

 mites, but other species have more y,^ 294.-Nymphon; a pycnogonid. (Original.) 

 pairs of legs; moreover, the seg- 

 mented body and the character of the mouth parts are greatly at variance with 

 acari. The male carries the egg masses attached to a special pair of legs. Many 

 genera and species are described, some occurring under stones near low-water 

 mark. 



COLLECTING, PREPARING, AND REARING MITES. 



If one desires to collect all kinds of mites, he must search every imaginable place. 

 Many students take up some particular group, more restricted in habits; thus if one 

 wishes to collect Analgesidse, he must examine bu*d skins; if he is seeking Eriophyidse, 

 he walks about looking for their galls; if he is after Hydra chnidae, with nets he must 

 examine the water of pools and streams. In general the free-li^'ing land mites are to 

 be found most abundantly on the ground among fallen dead leaves and in moss. This 

 material can be sifted through a small-mesh wire sieve onto a white cloth or paper, 

 where after a few minutes "plajdng possum" the mites will start to crawl away. They 

 can be picked up by a toothpick dipped in glycerin, or by a fine camel's-hair 

 brush, or many can be taken on the wetted point of a pair of fine forceps. Those in 

 hard fungi can be shaken from their retreats; those under bark can be observed by 

 use of a low-power lens; those on leaves and twigs of trees can be beaten into an 

 inverted umbreUa or piece of outstretched white cloth. 



Berlese has invented an apparatus for collecting mites and smaU insects in large 

 numbers. It is described and figured in Bulletin 67 of the United States National 

 Museum. The material — decaying leaves, moss, etc. — is placed on a sieve within a 

 funnel; the funnel is heated by a hotwater jacket; the mites, aroused by the heat, 

 fall through the sieve down the funnel into a vial of alcohol below, placed there for 

 that purpose. This method saves time, but one loses much of the pleasure of collect- 

 ing, and fails to learn the habits of the mites in natm-e. All mites may be collected 

 in alcohol of about 70 per cent. Many prefer to collect them alive and kill them by 

 special methods which will keep the legs extended. They can be killed in hot water 



