THE ISOPODA 201 



styles. The maxillipeds (mxp), which close the oral cone below, 

 have an elongated basipodite produced distally into a slender 

 endite, with many coupling-hooks ; the next segment is also pro- 

 duced distally as an acute, serrate point, and the remaining 

 segments of the endopodite are coalesced into a short palp. The 

 appendages of the second thoracic segment (II), which in this 

 family is coalesced with the head, lie on either side of the oral cone 

 and end in strong curved claws which no doubt assist in pene- 

 trating the skin of the host. The adult animals are free-living 

 and have the mouth-parts very differently developed in the two 

 sexes. In the male (Fig. 121, E) a pair of relatively enormous 

 mandibles (m) are articulated at the outer corners of the front 

 margin of the head and are apparently used only as defensive 

 weapons. The small aperture of the mouth is placed much further 

 back on the lower surface of the head. The maxillulae and 

 maxillae are entirely lost. The maxillipeds (Fig. 121, F) are broad 

 and flattened, composed of six segments tapering gradually to the 

 apex ; the endite of the basipodite is small and the other segments 

 are fringed externally with long plumose hairs. The appendages 

 of the second segment (Fig. 121, G) have lost the pediform 

 character which they have in the larva and in all other Isopoda, 

 and form a pair of overlapping valves closing over the oral area. 

 Each consists of a large oval plate showing traces of three segments 

 and bearing distally one or two minute terminal segments. In 

 feeding, these valves are opened out and the vibratory movements 

 of the maxillipeds produce a current of water which is supposed 

 to carry food -particles towards the mouth. In the female (Fig. 

 121, C) the mandibles have disappeared and the maxillipeds are 

 similar to but smaller than those of the male. The second 

 thoracic limbs (Fig. 121, D) are, however, very different, consisting 

 of a small leg-like appendage of three segments, having at its base 

 a large oval plate which probably represents an oostegite, although, 

 in this genus, distinct oostegites are not found on any of the 

 other limbs. 



In the Epicaridea the styliform mandibles are enclosed in a 

 suctorial " oral cone " formed by the upper and lower lips. The 

 maxillulae and maxillae are vestig';^ or absent, and the lamellar 

 maxillipeds serve, as already mentioned, to keep a current of water 

 flowing through the brood-pouch. In the ovigerous females of many 

 C ymothoidae the mouth-parts are covered by the anterior oostegites, 

 so that the animal is incapable of feeding, and in some genera of 

 Sphaeromidae the mouth -parts of the adult females (with the 

 exception of the maxillipeds) are reduced and functionless. 



The last seven pairs of thoracic appendages in the Isopoda are 

 typically developed as walking-legs which may, as in the Oniscoidea, 

 present a uniformity of size and shape justifying the name Isopoda, 



