84 Notes on the Development of Oerris najas. 



captivity, and between April 17th and May 4th five batches of 

 eggs were laid, with an average of eight in each. There was a 

 plant of Ranunculus aquatilis, having only fine cut leaves, in the 

 vessel, but the eggs were laid on pieces of wood floating on the 

 water, in three cases on the under side, and in one on the upper 

 side, the remaining one being doubtful. The eggs were clear 

 and transparent when laid, but eventually became darker, the 

 rich red eyes of the embryo being distinctly visible as they 

 matured. They were a long oval in shape, loosely laid, but all 

 in one direction, with their long axis parallel to the material on 

 which they rest. 



About three weeks after the eggs were laid the young larvae 

 began to hatch. When first hatched they swim about under the 

 water like a Corixa or Notonecta, but instead of using only the 

 posterior pair of legs as these insects do, they use both the 

 middle and posterior pairs, and they seem to have no controlling 

 power as to which side is uppermost. In the course of a few 

 hours the insect assumes its normal position on the surface of 

 the water. This change of position is accomplished very rapidly, 

 and seems to be effected by the insect rising as far as possible to 

 the surface, then by a kind of back-throw jerking its body out of 

 the water, then righting itself and withdrawing its legs. It is 

 interesting to note that this change cannot be accomplished if 

 the surface of the water is at all filmy or stagnant, neither will 

 the larva live if removed from the water. 



The young larva when first hatched is of a pale yellow-brown 

 colour, and the abdomen is much prolonged, comprising nearly 

 one-third of the length of the whole creature ; after a few hours 

 the larva becomes darker in colour, and the abdomen contracts 

 till it comprises scarcely one-seventh of the whole insect. As 

 the insect grows the abdominal segments gradually extend, until 

 in the pupa stage they amount to two-fifths, and in the perfect 

 stage as much as one-half of the whole. 



The perfect insects are very voracious, flies, spiders, &c., being 

 all greedily sucked ; they are gregarious, and the different stages 

 may be found together. The species is ordinarily apterous, but 

 Mr. Budgen informs me that he took one pupa with rudimentary 

 wings ; the imago which it produced was a cripple, but the mem- 

 branous wings as well as the elytra were clearly defined. This 

 is exceptional. (See Douglas & Scott, ' British Hemiptera,' Bay 

 Society, pp. 560—561.) 



I may add that I have found young larvae at various times all 

 through the summer, so that egg-laying continues for some 

 time after the above dates, which no doubt are some of the 

 earliest. 



