SOMITES AND APPENDAGES. 147 



{ex.})) ; but the former is singularl}' modified. The un- 

 divided basal part is large, and is produced on the 

 inner side into a lamella (a), which extends slightly 

 beyond the end of the terminal jointed portion (b). The 

 inner half of this lamella is rolled upon itself, in such a 

 manner as to give rise to a hollow cone, something like 

 an extinguisher {C, a). 



The appendage of the fiirst somite (A) is an unjointed 

 st3'liform body, which appears to represent the proto- 

 jiodite, together with the basal part and the inner pro- 

 longation of the endopodite of the preceding appendage. 

 The terminal half of the appendage is really a broad 

 plate, slightly bifid at the summit, but the sides of the 

 plate are rolled in, in such a manner that the anterior 

 half bends round and partially incloses the posterior half 

 They thus give rise to a canal, which is open at each end, 

 and only pai'tially closed behind. 



These two pairs of curiously modified appendages are 

 ordinarily turned forwards and applied against the sterna 

 of the posterior part of the thorax, in the interval be- 

 tween the bases of the hinder thoracic limbs (see fig. 3, 

 A). They serve as conduits by which the spermatic 

 matter of the male is conve3'ed from the openings of the 

 ducts of the testes to its destination. 



If we confine our attention to the third, fourth, and 

 fifth metameres of the abdomen of the crayfish, it is 

 obvious that the several somites and their appendages, 

 and the various regions or parts into which tliey are 



L 2 



