ANATOMY OF STYLETS OF CAMBARUS AND ASTACUS. Si 



is also of horny and not of calcified material and thus may the 

 better make a closure of the tubule. 



The living tissue of the stylet was found to be a loose areolar 

 mass full of blood spaces and covered by a thin epidermis that 

 makes the exoskeleton. This tissue filled the vacant space in the 

 external mass in Fig. 3. 



Excepting the muscles in the base that move the whole limb 

 upon the body there are no muscles within the stylet, but on the 

 other hand there are largely developed glands in the swollen 

 proximal parts of the spiral. These glands discharge through 

 the shell into the tubule not far from the orifice. 



In Camdarus dwgeues, which, belongs to the subgenus Bartonius,. 

 the stylets (Figs. 4 and 6) have a very different appearance owing 

 to great shortness of the terminal portion of the spiral. The 

 base and the neck remain much as in C. virilis, but the spatula 

 and the canula are very short and thick with the tips turned up 

 dorsally (Fig. 4). They are also much flattened, and are thus 

 very narrow as seen from the posterior face (Fig. 6). 



Practically the whole length of the canula and much of the 

 spatula are horny. A section across the canula (Fig. 5) shows 

 the shelf from the external mass [Ex.m.) and the isolated bottom 

 of the groove. It also shows that the median mass [M.m.) has 

 exaggerated the tendency seen in C. virilis (Fig. 3) to grow over 

 the groove, to such an extent that it runs over the shelf of the 

 external mass and so makes the closure of the tubule a very com- 

 plete one. 



The horny tip of the canula shows its finer structure more 

 readily than in C. affinis and we see under higher magnifications 

 that the horny substance presents lengthwise striations on the 

 surface, which at the tip give place to areolations suggesting 

 scales. Possibly this slight roughening of the tip of the canula 

 may be of some use in cleaning out the orifice of the sperm 

 receptacle. 



In the southern form, Cambarus Clarkii, the first stylet is the 

 antithesis of that of C. vinlis for the terminal parts of the spiral 

 (Fig. 7) are so greatly shortened as to form a flat mass that is 

 largely horny and though bent upward, somewhat as in C. 

 diogenes, more complicated at its tip. 



