55 E. A. ANDREWS. 



While the first stylets of both Cambanis and Astaciis show- 

 neither in their anatomy nor in their ontogeny any sign of 

 derivation from the typical forked crustacean limb this is not the 

 case with the second stylets. These remain forked in the adult 

 and we shall see that they arise from the modification of an ordi- 

 nary pleopod by the addition of a lateral outgrowth, while the 

 first stylet would seem to be derived by the dropping out of 

 part of the typical limb and by the condensation of the rest. 



The second stylet in Cambarus bears a setose exopodite and 

 endopodite that are fringed with setae and contain muscles that 

 move these forks of the limb upon the basal part. In the develop- 

 ment of the larva there is added to the simple limb an outgrowth 

 from the endopodite that finally becomes the peculiar excres- 

 cence characteristic of the second stylets of the crayfish. 

 These outgrowths are applied by the adult male against the 

 orifice of the first stylet and play an important accessory role in 

 the processes of sperm transfer. 



In Astacus the second stylet (Fig. 24) is much like that in 

 Cambarus. It has a slender exopodite ^Ex) and a wide endo- 

 podite {Eli) that ends in a setose filament {Fl^. But the lateral 

 outgrowth, or ekcrescence, is different. In Cambarus this part 

 may be called the triangle and it ends in a rounded free edge that 

 is inserted into the groove of the spiral of the first stylet during 

 sperm transfer. This thick edge is somewhat comparable to a 

 radius bone and ends with a hollowed head. Distal to this radius 

 the triangle is continued as a pyramid, bearing setae : this pyramid 

 we call the "wedge." 



But in Astacus (Fig. 24), the triangle (7)') suggests an extin- 

 guisher in form since the wedge {W") is a direct continuation of 

 the edge of the head of the radius in the form of a curved plate 

 as indicated in the smaller figure to the right. The wedge {W^ 

 is not a pyramid at all but a thin, rather pointed plate curved 

 around a deep depression to join the edge of the radius {R) as 

 shown in Fig. 24. 



of thorax 8 ram. (in alcohol), of telson fan ii mm., of telson 3.5 mm., of setse on 

 telson 1.5 mm., number of joints in antennse 75 plus. The stylets were about 2 mm. 

 and the second stylets 4 mm. apart. There was a rounded area and a dim white 

 organ within base of fifth leg, indicating the defferent ducts of the male, probably. 



