4 o the scottish naturalist 



Life-History. 



So far as our incomplete knowledge of the life-history 

 goes, there would appear to be four stages the egg, larva, 

 nymph, and imago. The eggs are almost without exception 

 enclosed in a gelatinous mass, which serves to anchor them 

 to the spot where they have been deposited. While the 

 gelatinous covering may to some extent act as a protection 

 to the egg during development, it is not proof against attack 

 by at least one species of Ostracod. 1 After the lapse of 

 varying periods, the hexapod larva emerges. The principal 

 object of the larva appears to be to find a host to which 

 it may attach itself by means of the relatively strong palpi 

 with which it is furnished. This stage is generally perhaps 

 not quite correctly called the parasitic stage. It is very 

 doubtful if the larva is really parasitic at all, as shortly after 

 attachment the limbs drop off and the larval body begins to 

 swell out owing to the development of the nymphal body 

 within. When mature, the skin is ruptured and the eight- 

 legged nymph emerges. The host is of necessity some 

 insect which either inhabits or spends part of its existence 

 near the surface of water. Consequently, during the 

 transition from larva to nymph, the mite exists for consider- 

 able intervals, i.e. during the flight of insects, out of the water, 

 and in this way in many cases the dispersal of species 

 may be accounted for. Nymphs may readily be distinguished 

 from adults by the presence of what has been termed a 

 provisional genital area. 



Classification of the Water Mite. 



It is beyond the scope of the present article to consider 

 the varied views of writers as to the position of the Acarina. 

 For our immediate purpose consideration will be limited to 

 the Hydracarina, 2 which a recent classification treats as 

 a suborder divided into three families the Halacaridao 

 inhabiting salt water, and the Limnocharidae and Hygrobatidae 



1 Proc. Roy. Phys. Soc, xviii. 92-94 



- Water mites were for long known as Hydrachnidre, but a more 

 suitable term is now employed, viz. Hydracarina. 



