226 THE MORPHOLOGY OF THE CRAYFISH. 



behind the liver. Rathke states that the sexual apertures 

 are not visible until the young crayfish has attained the 

 length of an inch ; and that the first pair of abdominal 

 appendages of the male appear still later in the form of 

 two papillae, which gradually elongate and take on their 

 characteristic forms. 



