Lobster — Appendages, Anatomy. 17 



with its gnathobase, and a small " palp " of three segments Wall- 

 representing the rest of the protopodite with the endopodite. ^^^^ . _., 



Tlie rest of the appendages may be briefly disposed of. The 

 icalking-legs (Fig. 1) can easily be seen to correspond, segment for 

 segment, with the third maxillipeds, except that they have no 

 exopodites. The large claws {chclipcds), like the two pairs of legs 

 immediately succeeding them, are chelate or pincer-like. This 

 modification, which is very frequent among Crustacea in limbs 

 used for seizing food, is brought about by the penultimate segment 

 of the limb growing out into a process, the " immovable finger," 

 lying alongside the last segment, which can be brought into con- 

 tact with it and is known as the " movable linger." 



The movable stalks, upon which the eyes are set, are divided 

 into two segments and in a few Crustacea they are even composed 

 of three. The view was long and widely held that these stalks 

 were the equivalent of a pair of appendages like the legs or jaws. 

 There are some reasons, however, for believing that this is not the 

 case, and the eye-stalks are therefore omitted from the list of 

 the Lobster's appendages given here. 



Some of the gills {branchiae) of the Lobster are seen attached 

 to the epipodites of the thoracic limbs. Their exact arrangement, 

 however, is more clearly shown by the preparations in spirit 

 exhibited alongside. In a transverse section through the thorax 

 it is seen that the gill attached to the epipodite of the leg lies on 

 the outer side of the branchial chamber. It is known as a 

 " podobranchia." Next to it on the inner side are two gills which 

 spring not from the leg itself, but from the membrane of the joint 

 between the leg and the body. These are called " arthrobranchiae." 

 Finally, next the inner wall of the chamber, is a gill attached to the 

 wall of the body itself and known as a " pleurobranchia." The 

 complete set of four gills is not present on every thoracic somite 

 and the arrangement differs very much in different Crustacea. 



Internal Anatomy. — The general arrangement of the internal 

 organs of the Lobster is shown by a preparation in which the 

 animal is dissected from the side (Fig. 4). The alimentary canal 

 liegins with a short gullet or " oesophagus " leading upwards from 

 the mouth into the large " stomach," from which the "intestine " 

 runs straight backwards to the vent on the under side of the 

 telson. The stomach is not very suitably named, for it is probably 

 not the place where the chief pi'ocesses of digestion go on, but on 

 the other hand it contains a complex apparatus known as the 

 " gastric mill " which acts as a gizzard in grinding up the food. 



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