June, 1917-] Hungerford: Life History of a Boatman. 119 



is no hint of the sexual dimorphism soon to be seen when the adults 

 arrive. 



Structural Changes in Development. 



In common with all the other water-bugs with which the writer 

 is familiar, the adults differ from the nymphs in the possession of a 

 larger number of tarsal segments. 



In this corixid it is interesting to note that the foreleg of the 

 nymph possesses one less than the requisite number of leg segments. 

 In the late fifth instar the terminal segment of the nymph may be 

 seen to contain the tibial and tarsal segments of the adult (see fig. 

 10). The middle leg has the same number of segments in the nymph 

 as in the adult. The tarsus of the hind leg is one-segmented and the 

 two segments of the adult can be seen within, shortly before trans- 

 formation. 



All the nymphs have two distinct claws on the hind tarsi. These 

 are very distinct in the first instar as shown in fig. 6. 



The antennae of the nymphs are two-segmented but four-seg- 

 mented in the adult. The terminal segment of the late fifth instar 

 nymph incases the three outer segments of the adult (PI. IX, fig. 15). 



The Adults. 



A technical description of this species is not attempted. Its limits 

 have not been defined, as yet, by Dr. Abbott, who is working on a 

 monograph of this difficult group. It is to be hoped that the above 

 mentioned monograph will be made available to the general worker 

 at an early date. At present we must content ourselves with indefi- 

 nite designations." 



The species whose life history is here presented is a common one 

 in our ponds and pools in Kansas. It is especially in evidence in the 

 clear small pools which in excessively dry seasons disappear. 



This corixid is of medium size and barred with a pattern of yellow 

 and brown. The arrangement of the darker pigment pattern being 

 delineated in fig. 2.^ 



Like other corixids, the males and females are to be distinguished 

 by the somewhat larger size of the female and by the peculiar asym- 

 metry of the abdominal segments of the male, as shown in the sketch 



7 Dr. Abbott has stated that this species is a member of the alternata series. 



8 Drawn for me by Miss Edmonson, a Junior in the department of Ento- 

 mology of University of Kansas. 



