NEPHROPS. 207 
one called the exopfodite and the inner termed the endopodite. 
Hence they are termed dcramous appendages. The ab- 
domen of /Vephrops, therefore, resembles that of a polychzete 
annelid in that it is divided into a number of segments, each 
of which bears a pair of biramous swimming appendages. 
In the part in front of the abdomen the segmentation 
cannot be traced by the sclerites for they are united, at 
least dorsally and laterally, into one sclerite, but the appen- 
dages still enable us to determine the number of segments 
which have become fused. From these we find that the 
Fig. 131.—AN ABDOMINAL SEGMENT OF NEPHROPS x 3. 
(Ad nat.) 
Tergon. 
Articular Facet. 
- Pleuron. 
Sternon. Arthrodial Membrane. 
thorax consists of eight segments and the head of five, 
which, with seven abdominal, gives a total of twenty seg- 
ments. The telson having no appendages, there are 
only nineteen pairs of appendages. 
Glancing at the thoracic and cephalic (head) appendages, 
we see that there are four pairs of legs preceded by a pair 
‘of pincers ; these are succeeded by a pair of foot-jaws, inside 
which there are no less than five more pairs of jaws; and, 
lastly, in front of the mouth there are two pairs of feelers. 
We can recognise at once that the appendages have altered 
considerably in form and function if they all were at one time 
of a common type. The evidence of development and of 
comparative anatomy leads us to suppose that the ancestors 
of lobsters had simple biramous appendages to each segment. 
All were used as swimming organs, but when walking on the 
