1922] Phases in tpie Development of Chrysemys Cinerea 59 



From present evidence it appears that there is also a considerable 

 difference in growth rate between the males and the females of C. 

 cinerea. The average size of the males taken during the two summers 

 was 117 mm., while the average for the females, for the same time, 

 was 143 mm. The largest female caught measured 187 mm., while 

 the largest male was 175 mm. Another fact which seems to sup- 

 port the idea is that the males become sexually mature by the time 

 they have reached a length of 88 mm., while no females have been 

 found which were sexually mature under 130 mm. A male turtle 

 was considered as being sexually mature when active spermatozoa 

 were found in the vas clef evens. Sexual maturity in the female is 

 indicated when the first set of eggs begins to enlarge. In the face 

 of these facts, one must assume that there is either a differential 

 growth rate or that the male matures several years earlier than the 

 female. It is to be expected that light will be thrown upon this 

 subject when the hundreds of turtles which have been measured, 

 tagged, and returned to the lake are retaken from year to year. 



It has not yet been determined when nor how the eggs are ferti- 

 lized. It seems a very difficult matter to collect C. cinerea in copulo. 

 Chelydra serpentina has been observed copulating in the laboratory 

 but this has not been observed for C. cinerea. A number of catches 

 were made in the lake when a male and a female were taken together, 

 plastron to plastron, the female being above, usually with the head 

 above water. These were supposed to be copulating. In all such 

 cases the males were much smaller than the females. Two copulating 

 seasons were observed during the year; one in the fall and another 

 in the spring. The opening of the spring copulating season is indi- 

 cated by the arrival well out in the bay of rather timid individuals. 

 Some of these have been caught with great difficulty and were found 

 to be males. As the season progresses, the females appear in the 

 swampy parts of the lake and are there sought out by the males. 

 Both males and females now become less timid and are easily taken. 

 Soon after the spring copulation laying begins. During September 

 and early October there is a similar congregation of individuals, and 

 spermatozoa can again be found in the oviducts which had been 

 free from them during the latter part of the summer. It was this 

 semi-annual copulation together with the appearance of the eggs in 

 groups that led Agassiz to formulate his theory of progressive ferti- 



