NEPHROPS. 213 
remains as a long, grooved spike, which apparently acts as 
an accessory organ of reproduction. 
In the female the next four are normal, but in the male 
the second one has a process of the protopodite which 
gives the whole appendage the appearance of being tri- 
ramous. The other three are normal. 
Fig. 142.—TuE First Pair oF 
SWIMMERETS IN NEPHROPS 
(3). (Ad nat.) 
Fig. 144.—A Tv- 
PICAL SwIiM- 
MERET OF 
NEPHROPS. 
(Ad nat.) 
Fig. 143.—THE 2ND 
SWIMMERET OF 
NeEPHROPS ( ¢ ). 
(Ad nat.) 
Protopodite. 
Protopodite. 
Spine. 
Protopodite. 
Endopodite. 
Exopodite. 
Endopodite. 
Note the spine on the 
Protopodite. eS 
In both sexes the sixth swimmerets are of large size, the 
exopodite being jointed. ‘These “paddles,” together with 
the median /e/son, form the tail which, on flexion of the 
abdomen, strikes the water forwards resulting in a rapid 
backward motion of the whole body.* 
At least four senses can be recognised in Wephrops. (1) 
The eyes are paired and situated just below 
the rostrum upon eye-stalks. They are called 
compound eyes. 
Compound eyes are characteristic of Arthropoda and 
have throughout the group a characteristic structure. They 
are called compound because they consist of an aggregate 
of elements called ommatidia, each of which has its own 
Exopodite. 
Sensory. 
* Lhe swimmerets in Astacus have the paddles (or exopodite and ,endopodite) 
differentiated into a basal unjointed and an upper filamentous portion. In Carcinus 
the swimmerets are vestigial ( g) or very reduced (@ ). 
5 
