CRUSTACEA. 289 



Palpi, arid sometimes the false feet. They 

 always exist in pairs, and take their rise from 

 the lower lip, or some adjacent part of the head. 

 The portions of which each is composed are 

 articulated together and moved by muscles in 

 the same manner as the ordinary or proper feet. 

 It is worthy of notice, however, that sometimes 

 the foremost pairs of palpi are shaped more like 

 jaws, and actually perform the office proper to 

 jaws, of compressing and dividing the food pre- 

 viously to its introduction into the mouth. These 

 auxiliary jaws are then called mandibles. In other 

 instances, we see them assuming every variety 

 of intermediate form between that of mandibles 

 and of false feet, so that it is often difficult, 

 amidst these gradual transitions of structure, to 

 decide to which of these two kinds of organs a 

 specimen we meet with properly belongs. It is 

 apparently with a view to evade this difficulty 

 that a term has been invented which shall in- 

 clude them all, namely, that of feet-jaws. These 

 transitions are illustrated by the annexed figures 

 of several of these members in the Mysis Fa- 

 bricii; Fig, 138 being that of a mandible, with 

 its feeler, or palpus; Figures 139, 140, and 141, 

 representing the first, second, and third pair 

 of feet-jaws; and Fig. 142, the first pair of 

 true feet. It would thus seem as if the same 

 constituent element of the fabric is converted by 

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