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. — The First Pair of 



SV^IMMERETS IN NePHROPS 



{6). {Ad nat.) 



Fig. 143.— The 2nd, 



Swimmeret of 



Nephrops ( 6 ). 



(Ad nat.) 



Protopodite. 



Fig. 144.— A Ty- 

 pical SwiM- 



M E RET OF 



Nephrops. 

 {Ad nat.\ 



Spine. 



. Endopodite. 



Exopodite. 



Note the spine on the 

 Protopodite. 



In both sexes the sixth swimmerets are of large size, the 

 exopodite being jointed. These "paddles," together with 

 the median telson, 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 Nephrons, (i) 

 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 



Sensory. 



* The swimmerets in Astac7is have the paddles (or exopodite and endopodite) 

 differentiated into a basal unjointed and an upper filamentous portion. In Cafcinus 

 the swimmerets are vestigial {$) or very reduced ( $ ). 



