Ixxxvi. PRESIDENT'S ADDRESS. 



the west, and it was rather a warm day for the season. Under 

 ordinary circumstances one sees a few of the water-boatmen 

 occasionally in the pond, but they never seem to be particularly 

 numerous. 



No further migration from this pond was observed until 

 October i ith, when, between eleven and twelve in the morning, 

 the day being warm and sunny, another smaller species of water- 

 boatman (Corixa Fabricii, Fieb.), was seen to be migrating in 

 considerable numbers, though not to the same extent as the 

 larger species in September. They continued until about 

 2 p.m., when the flight ceased. They did not swim to the 

 edge of the pond like Corixa Geoffroyi, but seemed to rise 

 straight from the bottom and fly up from the surface of the 

 water. They then circled round higher and higher until they 

 were lost among the branches of the surrounding trees, but 

 some, after taking a turn or two over the water, flew straight 

 away down the field in an easterly direction, the same as that 

 taken by the larger species. Whilst the flight was going on a 

 few of them paddled about on the surface in a sort of dance, 

 but these did not seem to fly away like those which came up 

 straight from the bottom of the pond. No migration of any 

 sort was going on in other ponds in adjacent fields. These 

 water-boatmen, like the rest of the winged Hemiptera, only 

 acquire wings in the last stage of their development, and the 

 probability is, therefore, that they were all bred in the pond 

 from which they migrated. It may be that they had only lately 

 passed the stage which corresponds to the pupa stage of a 

 butterfly, and that the recent acquisition of wings had something 

 to do with the strong impulse that had come over them to use 

 them. These insects are carnivorous, and it might well be that 

 they had cleared the pond of most of the suitable food, and 

 were driven by hunger to make their escape as soon as they had 

 acquired the means of doing so in the shape of wings. This 

 also furnishes an explanation of the two distinct migrations at 

 different times of the two different species, as it is likely that all 



