78 FIB8T LESSONS IN ZOOLOGY 



lime ; hence the lohster is called a "crustacean." But the 

 creature has feelers and legs, and the body must be movable 

 in its different parts ; hence the crust and the legs, etc., are 

 divided into rings or joints called "segments.'' Were not 

 the lobster thus ringed or segmented, it would be inclosed 

 in the straitest sort of jacket. Thus the body is composed 

 of a certain number of segments. 



Now let us see how the segments and their appendages look, and 

 finally we may estimate how many there really are, while we may 

 also discover a fundamental similarity in all the appendages. With 

 the point of a knife separate one of the middle segments of the hind 

 body (Fig. 81, ^or F). It forms a complete ring (Z>'), with the legs 

 attached to the under side. The pupil may next separate all the seg- 

 ments of the hind body and lay them upon the table in the order 

 given in Fig. 81, BtoG. Each segment will be seen to be much like 

 the other, and each to bear a pair of two-branched limbs. Each limb, 

 as in D', consists of three parts, i.e., a stalk (S), supporting an inner 

 (en) and an outer branch (ex). 



But the sixth ring (Q) will be somewhat of a puzzle to the begin- 

 ner. What are the broad, flat, fan-like appendages? Are they true 

 legs? Yes ; they may be directly compared with the legs immedi- 

 ately in front. They form broad paddles, which move up and down, 

 and propel the creature backwards. 



Still a greater puzzle is the piece S. Is this a part of the segment 

 G or not? It is in reality a partly formed separate segment, without 

 any legs, and is the last segment in the body. 



On counting the segments of the hind body the pupil will find that 

 there are in all seven, the last not bearing any legs. 



Now, before we try to find out how many more rings or segments 

 there are, let us look carefully at the head and chest (thorax). We 

 see that it is protected by a large shield (A), which ends in front in a 

 spiny beak (r). In little hollows on the front edge are the eyes (e), 

 which are very movable, being mounted on stalks. The eyes are 

 black; and when the creature is undisturbed they are held straight 

 out, but if frightened they are folded back in. the cavity, and thus 



Fio. 81.— External anatomy of the lobster. A. carapace; e, eyes; r, rostrum; 

 o', first pair of antennse; a', second pair; ft, outlet of green gland ; m, man- 

 dible, andp, its palpus; mx-^nuc', maxillse; mp first maxillipeae; mp', second 

 maxillipede; mp', third maxillipede: with ep, epipodite, and g, ?ill; i-d, first 

 leg; B-G, six abdominal segments; H, telson; B $ , first pair abdominal legs 

 of male; Bf.ot female; J), section of abdomen, with en, endopodite; ex, 

 axopodite' 6, basipodite; S, section of eye; /, cornea; e, cone; n, rod. 



