ANATOMY OF STYLETS OF CAMBARUS AND ASTACUS. 8/ 



•ception, there is nothing to suggest the minute inner part of the 

 groove of Cambarus and the large hole covered by the shelf must 

 be the homologue of the tubule of Cambarus. 



The obvious suggestion that the canula is derived from a rolled 

 plate is unfortunately supported by no actual observation, though 

 the few following facts regarding the development of the stylet in 

 A. leniusculus show a simple beginning that may well later suffer 

 a process of inrolling. 



A larva 19.5 mm. long, shedding from the fourth to the fifth 

 stage, showed on the cast the two minute papillae seen in Fig. 19, 

 growing toward one another on the ventral ridge of the sternum 

 of the first abdominal somite. That these are the first stylets of 

 the male is indicated by the fact that in larvse killed in the middle 

 of July and presumably in the fourth and fifth stages nine showed 

 110 outgrowths and were probably females while six showed out- 

 growths similar to these in Fig. 19. These little stylets differed 

 much in the different males. 



In larvae from 20 to 26 mm. long the stylets differed in size and 

 form from the state shown in Fig. 19 to that shown in Fig. 23. 

 The state of advance of the stylet was not parallel to the length 

 of the larvae, thus a male 26 mm. long had the stylet much as in 

 Fig. 19, while one 25 mm. long had them as Fig. 23. A male 

 20 mm. long had the stylets shown in Fig. 20 ; they were some- 

 what flattened papillae pointing toward one another. Fig. 21 

 shows the left stylet from a male 23 mm. long and Fig. 22 that of 

 a similar male. The most developed stylet (Fig. 23) is not only 

 flattened but its posterior face is somewhat concave and shows on 

 its median edge, to the left in the figure, a slight notch to repre- 

 sent the future neck (compare Fig. 14), while the median edge is 

 thickened as if it might grow up to form the enveloping median 

 mass to cover over the flattened or concave part that would be 

 the groove. The whole organ is then a stiff flat spoon and is 

 remarkably like the stylet of the American lobster in miniature. 



At the tip of the stylet is a minute protuberance tipped with a 

 spine and suggesting a sensory function (Fig. 23). This was 

 found on the stylet of the opposite side, but not in any of the 

 stylets of other males, which were all less advanced.^ 



1 The general proportions of the longest 26 mm. male may be seen from the fol- 

 lowing measurements : The length of antennae 26 mm., the chelae 18 mm., the width 



