CRUSTACEA. 269 



of a great number of pieces articulated together : 

 and they are infinitely diversified in their form in 

 the different genera and species, both of Crustacea 

 and of Insects. 



The jaws, and other parts connected with the 

 mouth, present a great complication of structure ; 

 and many of these parts are employed in various 

 uses besides those of mastication ; such as the seiz- 

 ing of objects, turning them in various ways for 

 examination, and, according to their suitableness as 

 articles of food, conveying them into the mouth. 

 These organs are called the palpi, and sometimes 

 i\\e 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 previously 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 the specimen we are examining 

 properly belongs. It is apparently with a view to 

 evade this difficulty that a term has been invented 

 which shall include them all, namely, that oi feet- 

 jaws. These transitions are illustrated by the an- 

 nexed figures of several of these members in the 

 Mysis Fahricii; Fig. 138 being that of a mandible, 



