1917] Studies on Hydromyza Confluens Loew 37 



water-lily beds. None were found on the petioles or other 

 parts of the white water-lily {Castalia odorata) although both 

 species of water-lily intermingle in the same beds. This restric- 

 tion of the eggs to N. americana accounts for the constant 

 relation of the larval and pupal stages to the same plant which 

 is discussed in the earlier paper (Welch, '14, p. 136). Appar- 

 ently, the female has the ability to recognize the food-plant 

 even in the presence of numerous other aquatic plants, some of 

 which present conditions similar to those of N. americana and 

 are closely related to it. 



Oviposition is constant with respect to the following fea- 

 tures: (1) The long axis of the egg is parallel to the long axis of 

 the petiole. (2) The surface of the egg in contact with the 

 petiole is always opposite the carinae and fossa. (3) The blunt 

 end of the egg is directed towards the rootstalk and the acute 

 end towards the leaf. 



Eggs may occur anywhere from the leaf attachment to the 

 rootstalk, even on petioles almost six feet long. As many as 

 seventeen were found on a single petiole, scattered over a 

 length of only one and one-half feet. An examination of a large 

 number of petioles showed that while eggs are deposited on 

 both the plane and convex surfaces, by far the greater number 

 occur on the latter. The significance of this decided preference 

 of the female in selecting the position of the egg is not known. 

 The egg is rather firmly fixed to the surface of the petiole, 

 apparently by a small amount of sealing fluid which accompanies 

 the egg at oviposition. As will be shown later, the position of 

 the egg determines the future position of the larva and pupa in 

 the petiole. 



As stated above, oviposition has not been observed and it is 

 not known whether the eggs which occur on a single petiole are 

 deposited by a single female or by several females. In the 

 earlier paper, the writer ('14, pp. 138-139) called attention to 

 the small variation in the maturity of the larvae and pupae and 

 suggested that possibly the eggs on a given petiole were depos- 

 ited at the same time by a single female. While this is still an 

 open question, counter-evidence was apparently secured when, 

 in the dissection of the ovaries of a considerable number of 

 females, collected during the time when eggs were appearing in 

 the field, it was found that no individual contained more than 



