THE CANADIAN ENTOMOLOGIST. 13 



Hydrometra has a very curious habit that I have frequently noticed. 

 It lowers its body by bending the legs, until it touches the surface, and 

 there it lies, as it were, taking its ease. I have also noticed aquarium 

 specimens putting out their hair-like rostra and penetrating the surface 

 film with them. It feeds on the insects that fall into the water and attacks 

 them even before they cease to struggle. In the latter case it is 

 extremely interesting to watch them stealthily approach their victim, 

 extending and retracting their long beaks, retreating hastily at some 

 sudden struggle of their prey, then once more resuming their cautious, 

 slow approach, until at length, when the struggles of their destined meal 

 grow feeble, some bold one injects into it the deadly poison of the 

 Hemiptera, stilling its motions, and the others then hasten to the feast. 

 As noted by Martin, several will fasten their beaks into one insect 

 simultaneously. 



Although Martin casts much light on it, especially on the oviposition 

 and kindred phenomena, the life-history of Hydrometra Martini is still 

 but imperfectly known. To his data my observations this summer enable 

 me to add one or two facts of interest. I have not witnessed oviposition 

 so entertainingly described by this author. 'I'iie ovum, however, I have 

 seen, and it is a most beautiful object under the microscope, answering in 

 every particular to the most excellent drawing of it in his paper. I was, 

 however, able to ascertain the period between mating and oviposition. A 

 bred virgin female was mated on July 26th with one of the wild males 

 taken in Staten Island in May of this year. It immediately began to 

 swell and on the 28th or 29th of that month the first ovum was deposited, 

 the female being then quite swollen with ova, and continuing oviposition 

 thereafter. The number of ova deposited by a single female in the course 

 of a summer, under favourable circumstances, must be large. The two I 

 kept alive of those taken in Staten Island oviposited continuously from 

 the beginning of May to tiie end of August, and although I did not count 

 them, the sides of the aquarium were thickly studded with the ova, and 

 they must have numbered hundreds. This is the more remarkable, when 

 we consider that the abdomen of a full-grown female is not much over 

 6 mm. long and the ova are between 2^4 and 3 mm. The period of 

 emergence varies with the temperature. In the cool days of spring it is as 

 long as 19 days; in midsummer I have had ova hatch in about nine to 

 ten days. The nymphal stages are five, and the time between moults is 

 about three days, giving about fifteen days for the nymphal instars. This 



