206 THB MECHANICAL FUNCTIONS. 



than one piece. The leg is usually divided into two pieces, 

 by a joint. The tarsus is terminated by a single or double 

 hook, and sometimes by a pincer, or claw. 



New organs, not met with among the Arachnida, are here 

 for the first time developed, namely, the Antennse^ of which 

 there is one on each side of the head. They are denomi- 

 nated, in popular language, the feelers; although it is more 

 than probable that they perform some function of higher 

 ^importance than that of conveying perceptions of mere 

 touch. The antennae consist of slender filaments, composed 

 of a great number of pieces articulated together: and they 

 are infinitel}^ 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, pre- 

 sent a great complication of structure; and many of these 

 parts are employed in various uses besides those of mastica- 

 tion; such as the seizing of objects, and turning them in va- 

 rious ways for examination; and, according to their suita- 

 bleness as articles of food, conveying them into the mouth. 

 These organs are called the Palpi, and sometimes ih^ false 

 feet. They always exist in pairs, and take their rise from 

 the lower lip, or some adjacent part of the head. The por- 

 tions 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 some- 

 times the foremost pairs of palpi are shaped more like jaws, 

 and actually perform the office proper to jaws, of compress- 

 ing 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 in- 

 termediate 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 apparent- 

 ly 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 annexed 

 figures of several of these members in the Mysis Fabricii; 



