C. D. SOAR ON HYDRACHNID.S. 319 



ing, and drawing these insects, the study of their life history 

 has not been altogether neglected. Notwithstanding the small 

 progress made with this part of the subject, a few words on 

 some points, personally observed, may not be without interest. 



To begin at the beginning, it is no doubt well known to all 

 present that the Hydrachnidae like other acarina have their life 

 history divided into four stages, viz., the egg, the larva, the 

 nymph, and the imago. These stages then will be taken in 

 order. First, the egg. In the window of my room there is a 

 row of glass tubes, about four inches by one in size. In each of 

 these is growing a piece of pond weed to keep the water fresh, 

 then when a number of water mites of one species have been 

 taken they are put into one of these tubes, the date recorded, 

 and a daily examination of them made. In several instances 

 ova were fortunately deposited in the tubes. Hydrodroma rubra 

 (De Geer) deposited eggs in batches, loose in the water, not 

 being anchored anywhere. They had so nearly the same specific 

 gravity as the water, that the movement in the water due to 

 the adults was sufficient to cause the eggs to rise now and 

 again nearly to the top of the tube. All the other mites, which 

 deposited eggs, attached them, either to the water weeds or on 

 the sides of the tube, by a gelatinous film ; the eggs were always 

 in clusters of ten, twenty, or thirty at a time, but there seemed 

 to be no rule as regards the numbers. To watch the gradual 

 alterations in these eggs, from the time of laying until the larva 

 broke through the gelatinous envelope, was very interesting; 

 but the time the eggs took to develop varied very much in 

 different genera, for instance : — 



Arrenurus caudatus (De Geer) took twenty-four days. 



Nescea carnea (Koch), twelve days. 



Diphdontus despiciens (Mull), twelve days. 



Eylais extendens (Miill), thirty-eight days. 



Hydrodroma rubra (De Geer), twenty-six days. 



These developments took place at different dates from March 

 to October, so it will be interesting to note, if these great 

 differences are peculiar to the species, or to the time of year. 



Secondly, the larva. — The larva is hexapod when hatched. 

 The larva of the different genera showed, as it was to be ex- 

 pected, different forms ; they also exhibited a great difference 

 in disposition. The larval forms of Nescea and Arrenurus kept 



