228 



THE CRUSTACEA 



is frequently absent, and, when present, is generally inconspicuous 

 and composed of few segments. 



The antennae (Fig. 132, a") when fully developed liave a 

 peduncle of five segments and a more or less elongated nagellum. 

 A scale or exopodite is never developed. A conspicuous conical 

 or spiniform tubercle on the second joint of the peduncle bears the 

 aperture of the antennal gland, indicating that the five segments of 



FIG. 136. 



Phronwna sedentaria. a, female ; b, male. A', antennule ; A", antenna ; D, intestine ; Dr, 

 gland in chela of sixth thoracic appendage ; G, genital aperturei of male ; H, heart ; A', 

 branchia ; i Kf, mandible; N, ventral nerve-chain; 0,|eye ; Ov, ovary. [.(Fr' 



the peduncle must be derived from the six-segmented condition by 

 a coalescence of two segments distal to the gland-opening, probably 

 the third and fourth. In many cases the antennules and antennae 

 are more strongly developed in the male than in the female sex, 

 and bear more numerous sensory setae. In some Hyperiidea 

 (Fig. 136) the antenna, though well developed in the male, is 

 represented in the female only by a rounded tubercle containing 

 the antennal gland on the front of the head. In some cases the 



