HUNGERFORD: AQUATIC HEMIPTERA.. 181 



which they present concerning form and function. The following species 

 were studied and figured: A'', lutea, N. raleighi, N. iindidata, N. varia- 

 bilis, N. iyisidata, N. glauca, N. mexicana, N. shooteHi, N. irrorata, N. 

 uhleri, and N. indica. Sufficient material of N. H7idulata, N. variabilis, 

 N. insiilata and N. irrorata were examined to indicate that the o\'ipositors 

 of these may possess specific differences. Kirkaldy long ago gave up the 

 idea of distinguishing the males by their genetalia, but it would be worth 

 while to look into this matter again. 



N. glauca, N. lutea, N. irrorata have long ovipositors and place their 

 eggs in plant tissues. The others merely affix them to the surface, at- 

 taching them there by means of a colorless, water-proof glue. See plates 

 XIX, XXI and XXII with accompanjing legends. 



Migrations. These insects habitually fly from their winter quarters 

 to their breeding grounds in spring, as has been noted long ago. There 

 are some very interesting notes on the migration of back-swimmers, one 

 so curious that it is reproduced in substance here: 



"In evening twilight of a pleasant September day, 1846, Sir Geo. 

 Simpson encamped for the night, on his route from Red river to the head- 

 waters of the Mississippi, in the \acinity of latitude 48' north and longi- 

 tude 95' or 96" west. While supper was preparing he perceived some- 

 thing falling on his hat like drops of rain; and as there were no clouds 

 to be seen, presumed that it could not be rain. On looking on the ground 

 near the fire he saw that the falling objects were winged insects, which, 

 although unable to fly, had life and motion. The number rapidly in- 

 creased so as to give great annoyance, and continued till the ground was 

 covered by the shower. On the following morning Sir George found that 

 this shower extended from 25 to -30 miles in the direction he was travel- 

 ing. No information as to its extent other directions. It was ob- 

 served that soon after the shower the weather changed from warm to 

 cold. It is therefore probable that the whole of this immense swarm of 

 insects encountered the cold current, and were paraUved and precipi- 

 tated thereby. They all died soon after falling. In no instance were they 

 seen to revive after coming into a warmer atmosphere." — Ayyier. Journal 

 of Science ayid Arts for November, 18Ji7. 



The above appeared in American Journal of Science and Arts for 

 November, 1847, by Prof. Forrest Shephard. It relates to the same mi- 

 gration that was mentioned by the wTiter in his quotation from S. G. 

 Simpson in a former paper. 



Means of Defense. All collectors, from Frisch, 1728, to present day, 

 testify to the stinging propensities of uncautiously handled back-s-wim- 

 mers. If handled carelessly, they pierce one with the stylets of their 

 beak, the burning, painful sensation of which may last for some time. 

 Doctors Riley and Johannsen considered it of sufficient importance to 

 figure the salivary apparatus of Notonecta in their "Hand Book of 

 Medical Entomology." 



Some species, N. variabilis, for instance, secrete, when handled, a 

 milky fluid which oozes from the sides of the thorax beneath the ^\^ngs 

 and at the base of the so-called coxal plates. This fluid reminds one of 

 a similar secretion of Gyrinids. 



Enemies. Predators as they are, their lives are in constant peril. 

 The newly hatched are eaten by their older brothers. Woe betide the 



