304 ZOOLOGY. 



reference to a common plan, from which each one diverges 

 in its own way. In this typical form (cf. fig. 150 [5]) we 

 have a proximal portion attached to the body, the proto- 

 podite. Distally this divides into two parallel branches an 

 endopodite towards the median line, and an exopodite move 

 lateral in position. All three of these are divided into few 

 or many articulating segments. A fourth portion, the 

 epipodite, which comes off from the protopodite, is unjointed, 

 turns up dorsalwards, and may carry a gill. 



The protopodite is usually divided into two joints, of which the 

 proximal is called eoxopodite, the distal, basipodite. The endo- and 

 exopodites may have an indefinite number of divisions, but in several 

 cases the former has five : these are then termed, in order from 

 proximal to distal ischio-, mero-, carpo-, pro-, and dactylo-podite. 



The nineteen pairs of appendages are as follows. The 

 first two pairs are at the anterior end of the body, and 

 modified to serve as " feelers " or antennae ; the next three 

 are set close round the mouth to serve as jaws, the third 

 being called mandibles, the fourth and fifth maxillae. The 

 next three (6, 7, and 8) are intermediate in character 

 between these jaws and the walking-legs behind, and are 

 therefore called maxillipedes (fig. 150). Next comes the 

 biggest of all the appendages, the strong pincers ; followed 

 by four pairs of walking-legs (fig. 148). Lastly we have 

 the abdominal appendages, the first of which is vestigial in 

 the female, and forms a stout style in the male ; the next 

 four (fig. 149) are swimmerets (though the first of them in 

 the male is also modified) ; and the last form the lateral 

 portions of the tail-fin (fig. 148), the central part of which 

 is formed by the telson 



6. Head Appendages. The general form and appearance of 

 these various appendages is shown iu figs. 148, 150, and 158, and 

 the following notes on their peculiarities are only intended as an 

 assistance to the practical examination of them. All are, of course, 

 paired, although spoken of in the singular. 



The antennnle has a protopodite of three joints : both endo- and 

 exopodite are many-jointed and whip-like. 



The antenna bears on its coxopodite the excretory aperture ; 

 its exopodite is a flat, sharp-pointed plate, called the sguame ; its 

 endopodite is long, many-jointed, and whip-like. 



