132 



NATURAL HISTORY. 



a squarish pear-shaped body, upon which two parts may be recognised, a small anterior and inferior 

 portion bearing the eyes, the organs of the mouth, and the first two pairs of legs, and a larger 

 posterior portion, on the under surface of which, at some distance from the others, the 

 third and fourth pairs of legs are situated. The whole Mite is of a bright scarlet 

 colour, and the larger hinder part shows a beautiful velvety texture. This Mite may 

 be often seen running about upon the ground, in moss upon the roots of trees, <fcc., 

 and it is exceedingly rapid in its movements. In a young stage, it passes a certain 

 period as a parasite upon the long-legged Harvest Spiders (Phalangiuni), usually 

 selecting the females, and attaching itself behind the hinder coxae, where it is out of 

 reach. In this situation it remains, although capable of some amount of movement, 

 advance more and more towards the front as the animal grows. When 



TROMKIDIUM 

 HOLOSERICEUM. detached from the Harvest Spider, it conceals itself in the ground, and becomes an 



oval nymph, within the skin of which the eight-limbed perfect Mite may be watched 

 in process of formation. The change takes about three weeks. Other species of the group attach 

 themselves to insects of various kinds to undergo this nymphal change, and, as all of them attack 

 and destroy Aphides, and other minute insects, they must be regarded to a certain extent as our 



friends. 



FAMILY III. HYDRACHNTP^E, OE WATER MITES. 



These creatures may be regarded as aquatic representatives of the Trombidia, as they resemble 

 these in many characters. They have usually a more globose form of body, and there is no trace of 

 its division into two parts ; the 

 cheliceraa are similar; the palpi 

 terminate in hooks or bristles ; and 

 the legs, which generally increase in 

 length from the first to the fourth 

 pair, are strong and fringed, and 

 terminated by a pair of claws. They 

 have two ocelli on the fore part of 

 the body. 



These Mites, which are gener- 

 ally of tolerable size for their order, 

 a sixth of an inch being a common 

 length, live habitually in water, 

 many of them swimming with great 

 ease and considerable rapidity, while 

 some prefer crawling upon the 

 bottom. Some of them even live in 

 the sea. Although they remain con- 

 stantly under water, and apparently 

 never come to the surface to breathe, 

 they possess no recognisable bi-an- 

 chial organs, but are furnished with 

 the usual tufts of tracheae, opening 

 by stigmata placed between the fore 

 legs. Under these circumstances it 

 is rather difficult to understand how 



THE METAMORPHOSES OF HYDRACHNA GLOBULUS. 



1, The perfect mite, natural size and magnified: 2, the larva, magnified : 3, a nymph: 4, a 

 nymph, magnified, showing the eight-legged mite within ; 5, the last form of nymph, 



magnified. 



they carry on their respiration, .and 



some naturalists have suggested 



that their tracheae must be enabled 



to respire the air dissolved in the surrounding water. Of this, however, there is, we believe, 



no evidence. The young differ very materially from their parents. Like other young Mites they 



have only three pairs of legs, but they are also provided at the fore part with an enormous suctorial 



organ, by means of which they attach themselves as external parasites to aquatic insects of all sorts. 



