206 THE AMERICAN NATURALIST. [Vol. XXXVIII. 



showed a sperm plug as it did not before. When they were 23 

 months old they both laid eggs. 



Amongst the females that laid eggs in captivity there were 

 both long specimens 120 mm. long and smaller ones down 

 to even 75 mm. From their size we infer these small ones 

 were about to begin their third summer. Thus though the 

 sexual unions take place at the end of the first summer we 

 have, as yet, no evidence of eggs being laid till the begin- 

 ning of the third summer. However the autumnal union in 

 the first year was found not only in the specimens reared in 

 confinement but among those eighty above mentioned as taken 

 in the open. And here it occurred both in the laboratory and 

 in the pond and not only between the larger, third year sizes 

 but between those of 56 mm. which, probably, were in their first 



We see then that little specimens of C, affinis may have 

 mature sexual instincts and unite in pairs in the autumn when 

 they are but 4 months old and 50-60 mm. long, but as yet it is 

 not known if they lay before they are 23 months old and 

 75 mm. long. 



Finally. — In connection w^ith the development of sexual 

 maturity we may here refer again to the apparent sexual dif- 

 ference in lengths of antennae noticed in connection with tables 

 I and II. When the above 80 crayfi.'ih taken in the Autumn 

 and thought to be most all of the first year, like those of the 

 tables, were measured little difference between the lengths of 

 the male .and female antennae was found. Throwing out the 

 specimens with broken antenna? there were 37 males with an 

 average length of antenna of 42 mm. and 36 females wdth an 

 average length of antenna of 41 mm. Again the average male 

 antenna was 8 [.3 7; the average length of the male body while 



here not enough evidence that the females have the shorter 



