50 KANSAS UNIVERSITY QUARTERLY. 



Doctor Hagen made an anatomical examination ^ of first- and sec- 

 ond form males of C. acutus Girard, C. virilis Hagen, and C. hartonii 

 Fabricius. His observations were made from a very limited number 

 of specimens — probably only two from each species — and no note 

 was made of the time of year the material was taken, a factor the 

 significance of which he seems to have entirely overlooked. His ob- 

 servations were that the testis was decidedly larger in the first- than in 

 the second-form. He says, in fact : "The sexual parts of the second- 

 form males are so much less developed that it would be allowable to 

 consider them as sterile." Hagen's idea was that in the older males 

 of the second-form the sexual organs have failed to develop and are 

 consequently non-functional. He says: "But the great number of 

 full-grown second-form specimens in every species, which are often 

 even larger than the first-form males, seems to prove that they are in- 

 dividuals which have remained in a sexual stage that does not agree 

 with their corporal development — in short, they are, perhaps, sterile." 



The size of the arthroiDod testis, in fact, depends largely upon 

 the condition of the elements, being, for instance, larger when the 

 sperm-cells are in the spermatocyte stages than when the spermatozoa 

 are mature, and being, of course, smaller still after the testis has been 

 evacuated. 



So far as I have been able to observe, the testis of first- and second- 

 form males of the same size, taken at the same season of the year, are 

 equally developed, it being impossible to determine from an exami- 

 nation of the testis alone whether a given individual is first- or second- 

 form. 



Faxon*^ observed that the so-called first- and second-form males 

 merely represent alternating stages in the life of the individual. 

 Specimens of C. rusiicus Girard kept in his laboratory copulated 

 freely. Shortly after they exuviated, and, while yet soft, they were 

 thrown with their casts into alcohol. Upon later examination, it was 

 observed that the casts were first-form — the form in which the animal 

 had approached the female — while the animals themselves were sec- 

 ond-form. 



The same was noticed for a specimen of C. propinquus Girard 

 which had been preserved with its cast. 



I have had the opportunity of watching quite closely a small stag- 

 nant pond near Lawrence, Kan., in which occur C. gracilis Bundy, 

 C. virilis Hagen, and C. immunis Hagen. As C. immunis was by 

 far the most abundant, observations were made on it. In the late 

 summer and autumn, the proportion of first-form males gradually in- 

 creased ; there seems to be, so far as my observations go, no definite 



7. Hagen, loc. cit., pp. 22-24. 



8. Faxon, "On so-called Dimorphism," etc. 



