164 MR. G. C. BOTJIINE OK THE 



In tte male three pairs of accessory copulatory appendages are 

 inserted between the twenty-first pair of walking-legs and the 

 anus. Although these appendages have been described by Eabre, 

 and more fully by Karsch, these authors have overlooked several 

 points of importance connected with them. 



These three pairs of appendages in the male are clearly acces- 

 sory appendages developed in connexion with sexual functions, 

 and have no connexion with the segmentation. Whereas each 

 pair of walking-legs has a ganglion developed on the ventral 

 nerve-cord in connexion with it, the copulatory appendages have 

 no ganglia proper to themselves, but are innervated from the 

 twenty-first ganglion (see fig. 14) of the ventral chain; and 

 whilst a pair of tracheal openings corresponds with each pair of 

 walking-legs, there are no tracheae in connexion with the copula- 

 tory appendages. 



The first pair of copulatory appendages is small, and each limb 

 is three-jointed. The first joint is small, and flattened from side 

 to side. The second joint is the largest of the three, and poste- 

 riorly is produced into a claw-like process. The third joint is 

 hinged upon the base of this process, and closes upon it to form 

 a chela. In this way a simple pair of weak pincers is formed in 

 S. retusum ; but in S. obtusmn the chela is modified to form what 

 I believe to be an accessory stridulating organ. A hood-like 

 projection is developed from the third joint (fig. 2, a^), with its 

 concavity turned toAvards the claw-like process of the second 

 joint. The interior concave side of this hood-like process bears a 

 number of parallel ridges which work against the claw of the 

 second joint, and in so doing produce a slight grating sound. The 

 articulation between the second and third joints is of such a kind 

 that they do not act together as pincers ; but only a lateral 

 motion of the third joint across the claw of the second is possible, 

 whereby the stridulation above referred to is effected. 



The second pair of accessory appendages is much stouter than 

 the first ; as in them, each limb is three-jointed, and the second 

 and third joints together form a strong pair of pincers, called by 

 Eabre the forcipules copulatrices. The shape of these chelae dif- 

 fers somewhat according to the species ; and hence they are of 

 specific value. Pig. 3 is a representation of the chelae of S. oh-r 

 tusuvi, and figs. 5 and 6 represent those of S. retusum. 



Although Karsch has described these ap)pendages somewhat 

 minutely, and has given figures of their forms in difterent spe- 



