HUNGERFORD: AQUATIC HEMIPTERA. 231 



mediately became silvery. From the behavior of young Corixids, it would 

 seem that respiration must take place through the skin for they seldom 

 come to the surface, yet in the few experiments tried it was not demon- 

 strated that air was taken up in that manner. The nymphs were able to 

 5ur\-ive for many hours in cloth covered jelly glasses submerged in water. 



Number of instars. There are five njTnphal instars, which are shown 

 on plate XXVI. 



Maturity. This could not be determined from the overwintering 

 adults and was overlooked in the summer. The laboratory notes were 

 obtained from a start of nine indi\iduals that were placed in a large 

 circular aquarium April 3. Seven of these were females. By the last of 

 the month there were but three indi\iduals remaining, and May 9 only 

 two were left, but first instar nymphs had appeared. Some of these 

 changed to second instar nj*mphs May 12, and reached the fourth instar 

 June 2. The two overwintering adults were still alive and laying eggs. 

 June 10 found all stages from first instar to the fifth present. June 14 

 the first one of the spring generation reached the adult stage, followed 

 by another on the 19th. There were still first instar forms present. In 

 fact, eggs and newly hatched were present up to July 18. Since the 

 overwintering adults were not removed, it is impossible to say whether 

 the young represent a second generation or merely a continuation of the 

 first. The hot weather of the last week in July brought the rearing to a 

 close, and was valuable only in giving all the nymphal instars for study 

 and establishing the approximate time for the emergence of the spring 

 brood. It is certain that the adults of one year may live to see adults of 

 the next. 



Parasitism. In Bool's Backwater, where this Corixid was found 

 throughout the spring in company with the nymphs of Palmacarixa 

 bueyioi, the infestation of Hydrachnids was heavy. On May 9 a large 

 catch of this species showed 85 per cent of the bugs infested with one or 

 more mites, some of them with a dozen. May 15 there was not an adult 

 to be found that did net bear mites. On June 8 the mites freed them- 

 selves from their hosts in the laboratory, and on examination of the in- 

 sects in the pond June 11 found the boatmen much less burdened than 

 before and almost entirely free June 13. June 18 not a single "mited" 

 Corixid was noted. 



I'ESCRIPTION' OF STAGES. 



The following brief description of size and color is given for com- 

 parison with P. buenoi of same pond. The structural comparative studies 

 of njrmphs of various species are resers'ed for a future paper. 



The Egg. 



Size. Diameter, 0.369 nun.; height, 0.372 mm. 



Shape. Variable, depending on development of embryo within. In 

 general cvoid, but with the usual greater convexity of one side. 



Color. Pearly white when first laid, darkening to yellow. There is a 

 hexagonal reticulation plain to see under high power and proper lighting. 



