80 E. A. ANDREWS. 



We will first describe the stylets of Cambarus and then those 

 of Astacus. 



In these reduced limbs (Figs, i and 2) we may distinguish the 

 base (5), the neck (iV) and the spiral (5) which is the region 

 with a somewhat spiral lengthwise groove bounded by hard 

 rounded edges that run out to form the two tips of the whole 

 organ. It is this bifid appearance of the limb which has been 

 most emphasized in descriptive work. One of the tips may in 

 this species be called the spatula {Sp) from its shape. The other 

 tip (C) may be called the canula, as it is a termination of a tube 

 and is inserted into the sperm pocket of the female and allows 

 the sperm to pass out of its tip. Of the two apparent tips of the 

 limb, one, the spatula, is thus a side outgrowth of minor im- 

 portance ; the other is the real morphological and physiological 

 end of the organ and of fundamental value. 



The groove that runs along the length of the spiral region 

 begins at an orifice {Or') and ends at the extreme tip of the canula. 



We may regard this groove as dividing the spiral region into 

 two parallel portions, the external mass (^Ex.m.) and the median 

 mass {M.m.), external and median being used with reference to 

 the median plane of the entire animal. 



In Cambarus virilis (Figs, i and 2) the stylet is exceptional in 

 the great elongation of the spiral region, the spatula being very 

 much prolonged and the canula a curved, ovipositor-like struc- 

 ture. The tufts of setae at the junction of neck and base and 

 upon the median mass near the orifice are also long. 



Cross-sections (Fig. 3), at the level 3 of Fig. 2, show that the 

 external groove of the canula passes deep into the interior and 

 has its inner end partly cut off as a tubule by a ridge or shelf 

 which projects like a valve from the side of the groove. Serial 

 sections show the same general facts throughout the length of 

 the spiral. There is thus a continuous tubule from the orifice to 

 the tip of the canula. 



While the stylet has most of its exoskeleton firmly calcified, 

 as represented by the black in the section, the tips of the spatula 

 and canula are partly horn-like. In the median mass this horn 

 extends some distance toward the base, as represented in the 

 dotted area in the figure. The shelf that overhangs the tubule 



