Sept., 1917.] Marchand: Notes on Early Stages of Chrysops. 151 



the under side, seldom on the upper side of leaves, a difference which 

 is not marked in the case of vertically growing plants, such as Typha, 

 Sparganium, etc. They are usually found at a height of 6 inches to 

 2 feet above the surface of the water, never on plants which grow 

 any great distance from the water. It seems that in the choice of its 

 laying-place the female is somehow attracted by the sight of the 

 reflecting water-surface. 



The plants on which the eggs are found deposited are of a great 

 variety, including Pontcderia cordata, Nuphar spec, Peltandra 

 (Aroidecr), Typha latifoUa and angnstifolia, Acorns calamus, vari- 

 ous Graminea;, Polygouaccce and Equisetmn sp. No special prefer- 

 ence was shown for any of these, except that where TypJia was most 

 abundant the eggs were nearly all found on Typha ; while where 

 Pontederia was common there seemed to be more egg-masses on 

 Pontcderia than on any other plant. Most of the egg-masses seen 

 in the field certainly belonged to C. callidus, but it is not impossible 

 that some, while not differing in appearance, may belong to other 

 species of Chrysops. The Chrysops egg-masses were never found 

 on wood or on stones; the species show a decided preference for laying 

 on plants. The egg-laying instinct is, therefore, apparently deter- 

 mined by two factors : the presence of water and the presence of 

 plants growing above its surface. The egg-masses appear much less 

 numerous in places like Plainsboro, where considerable areas are of 

 a swampy character, evidently because the conditions for oviposition 

 are here evenly distributed. In places, however, where the swamp- 

 vegetation has been artificially removed, as in the case of Lake 

 Carnegie and of the little pond near Guyot Hall (Princeton Univer- 

 sity grounds), the plant growth is developed only at the edges and 

 it is on these alone that the conditions for oviposition are found. 

 This, perhaps, accounts for the large numbers in which the Chrysops 

 are ovipositing here and this phenomenon provides a favorable oppor- 

 tunity for the study of their life-history. 



The time of oviposition is, in Chrysops callidus, the morning, from 

 8 to 12 o'clock; and the largest number is found ovipositing between 

 10 and II o'clock. Only very exceptionally I found C. callidus ovi- 

 positing at 4 o'clock in the afternoon. The habit of laying in the 

 forenoon differentiates it sharply from the other species observed 

 which lay in the late afternoon. The eggs are creamy white at first, 



