. Elementary text-book of zoology. NEPHROPS. 207 one called the exopodite and the inner termed the endopodite. Hence they are termed biramous appendages. The ab- domen of Nephrons, 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. Fr
. Elementary text-book of zoology. NEPHROPS. 207 one called the exopodite and the inner termed the endopodite. Hence they are termed biramous appendages. The ab- domen of Nephrons, 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 Pleuron. 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. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Masterman, Arthur Thomas. Edinburgh, E. & S. Livingstone
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