SOMITES AND APPENDAGES. 147 
(ex.p); but the former is singularly 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 first somite (A) is an unjointed 
styliform body, which appears to represent the proto- 
podite, 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 partially 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 conveyed from the openings of the 
ducts of the testes to its destination. 
If we confine our attention to the third, diatith, 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 they are 
L 2 
