224 
bulletin of the bureau of fisheries. 
Table 4. — The Body Segments and Appendages of the Lobster with 
Divisions of body. 
Abdomen (7). 
No. of 
somite. 
Name of somite. 
Name of appendage. 
Functions of appendage. 
XV 
Modified in male for copulation, and re- 
duced in female to prevent attachment of 
eggs. Unirainous. 
Biramous; for forward swimming; in female 
for holding and aerating the eggs, and pos- 
sibly for secreting the glue by which they 
are fastened to certain of the setae; tactile, 
with chemical sense in doubt. 
XVII 
XIX 
XX 
XXI 
Sixth abdominal 
Sixth pleopod, or uro- 
pod. 
Enlarged and modified for forming with 
telson, the tail-fan, for backward swim- 
ming; tactile. 
In the typical thoracic leg (pi. xxxviii) the endopodite is divided into 5 segments, 
which, with the two divisions of the protopodite, give the limb 7 podomeres, numbered® 
and named from base to apex as follows: (1) Coxa or coxopodite, (2) basis or basipo- 
dite, (3) ischium or ischiopodite, (4) meros or meropodite, (5) carpus or carpodite, (6) 
propodus or propodite, and (7) dactyl or dactylopodite. These successive segments 
are articulated to the body and to one another by soft membrane and usually by hinge 
joints which limit the movements of each to a single plane at right angles to the articular 
axis, or to the line joining the two hinges; each segment, with the exceptions to be 
noted later, is actuated by opposing muscles, a larger flexor and a smaller extensor, the 
fibers of which are implanted over the hard shell of their respective segments and are 
inserted on strap-shaped tendons which react on the distal podomere (fig. 1, pi. xli). 
The tendon is derived from an ingrowth or flattened pocket of interarticular membrane 
(fig. 2, mb., pi. xli, and fig. 1, tp., pi. xliii), and is sometimes closely united to the shell of 
the distal segment. Each joint or articulation is therefore crossed by tendons which 
belong to the proximal podomere and pull on the distal one. 
In the successive somites of the tail the axes of articulation are all parallel, and 
at right angles to the longitudinal axis of the body so that movement is limited to the 
vertical plane. In the appendage, on the other hand, the direction of the axis of articu- 
lation varies in successive podomeres (see figs. 6 and 7) ; moreover the initial direction of 
movement of the base of each limb, which depends upon the angle which its articular 
axis makes with the long axis of the body, varies greatly from head to tail (135 0 in the 
mandibles, about 55 0 in the great chelipeds, and 90° in the swimmerets). Accord- 
ingly each segment acts as a lever of the third order, and the successive thoracic limbs 
are capable of universal movement, and in a variable field. By reference to figures 
a This order seems preferable to the reverse, which is sometimes adopted, since the protopodite has been less modified 
than either of its branches, and we thus avoid the ambiguity of speaking of the seventh segment of a pleopod or of an 
antenna 
