NEPHROPS. 207 



one called the exopodite and the inner termed the efidopodite. 

 Hence they are termed biramous appendages. The ab- 

 domen of Nephrops, therefore, resembles that of a polychaete 

 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 f. 

 (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 



