24 CRUSTACEA. 



The first pair of walking-legs (Fig. 8, B, e i ) have 

 become modified into large arms. The fifth section 

 (v). which corresponds to the sixth of the other walk- 

 ing-legs, is here greatly developed ; and it is, appar- 

 ently, the outer and not the inner portion of this 

 section which is prolonged to form the fixed jaw. 



Here, as elsewhere in nature, things are not always 

 what they seem. The big arms in the young are legs 

 precisely similar to the others, but, subsequently, during 

 growth, they are stretched out forward, and used hori- 

 zontally for grasping, and not used for walking. This 

 constant effort through many generations has doubt- 

 less caused them to assume the permanent twist which 

 the joints exhibit in the lobster, and which brings the 

 movable jaw inside instead of outside, as it is in the 

 second and third pairs of walking-legs. 



The inner edges of the jaws (it may be either the 

 •right arm or the left) bear large, blunt teeth, while 

 those of its opponent are small and sharp. The lob- 

 ster sometimes anchors itself by the blunt-toothed jaws, 

 which are usually the largest, while it catches and holds 

 its prey with the others. It also uses the large jaws, if 

 necessary, to crush and kill the live prey which is held 

 by the small ones. Most probably, some of the speci- 

 mens will show a very great difference in the size of the 

 two arms, as it is by no means uncommon for the lob- 

 ster to lose these appendages and then redevelop them. 

 Dr. Stevenson* relates that a lobster taken prisoner 

 by one of his arms sometimes leaves it in the hands of 

 his astonished captor, and beats a hasty retreat ; and 

 that he has also been known to shake off his arms when 



* "Boys and Girls in Biology,'' Chap. VII. 



