THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBARUS 67 



male and in female are first well seen in the fourth stage when the female still 

 bears minute tubercles and the male long papillag to represent the appendages of 

 this somite. From that time on to the autumn the distinctive characters of the 

 sexes become perfected so that the annulus of the female is much like that of 

 the old crayfish, and the first abdominal appendages, or stylets, of the male are 

 also much like those of the full grown crayfish. It is thus very easy to recog- 

 nize the sexes by external characters when they are four months old. The 

 actual length in millimeters of the male stylets in crayfish of four months is 

 given in the following table: 



Length of body . . . 55 53 49 45 43 60 52 52 45 39 40 33 30 

 Length of 1st stylet . 9 9 9 8 7 10 9 9 7 6 6 5 4 

 Length of 2d stylet . 10 10 9 7 11 10 10 8 7 7 5 4 



The second stylets are thus longer than the first and as much as 18 per 

 cent to 20 per cent of the length of the body so that the stylets are in about the 

 proportions they will be in larger crayfish since specimens 115 mm. long have 

 stylets 18 and 22 mm. long. 



Some examinations of various catches of adult crayfish indicated that there 

 is no great disparity in number of males and females and though it is not 

 known whether one sex or the other is subject to greater mortality in early 

 larval life, the following observations tend to show that the sexes are about 

 equal when four months old so that it may be that the eggs are about equally 

 male and female. Observed at four months: of 26, there were 15 male and 11 

 female; of thirty, 11 were male and 19 female; of 7, 4 were male and 3 

 female; of 19, 10 male and 9 female; of 10, 8 male and 2 female; of 8, 

 5 male and 3 female. Of the entire 100, 53 were male and 47 female. 

 With no marked disparity in numbers and with well formed external 

 organs the two sexes when four months old and about two inches long often 

 have well developed sexual instincts. Thus in October a male 55 mm. long, 

 1 5 mm. wide, with tail fan 22 mm. wide, antennae 48 and 51 mm. long and entire 

 expanse from tip of chela? to end of telson only 75 mm., was seen to try to con- 

 jugate with a sister 62 mm. long when four months eighteen days old. An- 

 other female had a mass of sperm transferred to its annulus by a male of like 

 age when four months old and 57 mm. long. Many cases were seen in which 

 the four months young had conjugated, thus of 19 females four months old, in 

 one aquarium, five bore sperm given by males of like age. Though the sperm 

 transferred by these young males was apparently perfect it seemed doubtful 

 if these unions would lead to fertile eggs but when a number of four months 

 females thus provided with sperm by males of like age were kept isolated from 

 all males during the winter they laid eggs in the spring which developed and 

 thus demonstrated not only that the females could lay eggs when but a year 



