The Lobster as a type of Crustacea. 13 
which, in the case of the body, are termed body-segments or 
“ somites.’' 
A study of the various modifications of structure presented by Wall- 
Crust acea and other Arthropoda has led to the conclusion that g 
they are to be regarded as built up of a series of somites or body- 
segments, which may be distinct or soldered together, and each of 
which bears typically a single pair of limbs or appendages. 
Thus, in the Lobster (Fig. 1), the hinder half of the body (or 
abdomen) is plainly made up of six somites (besides a tail-piece or 
The Common Lobster (Homarus gammarus ) . Female, from the side. 
[Wall-case No. 1.] 
f telson ”), each of which carries on the under side a pair of 
“ swimmerets.” The front half of the body is not so divided, but 
is covered by a large shield or “ carapace ” which projects between 
the eyes as a toothed beak or “ rostrum.” Since, however, this 
part of the body also bears a number of appendages constructed 
on the same plan as the swimmerets of the abdomen, it is con- 
cluded that here also we have to do with a series of somites, 
although they are so completely fused together as to be indistin- 
guishable except by their appendages. That this conclusion is 
correct is proved by comparison with some of the lower Crustacea, 
for instance, Anaspides (see Table-case No. 5), in which there is no 
