AN INTRODUCTION TO ZOOLOGY 



--ex. 



FIG. 102. Types of crayfish appendages. 

 A, second maxilla, foliaceous type ; 

 1-4, basopodite ; 5, endopodite ; 

 6, exopodite ; ep., scaphognathite. 

 (From Cambridge Natural His- 

 tory.) B, swimmeret, biramous 

 type; ex. bs., protopodite; 

 ex., exopodite ; en., endopodite. 

 (From Lankester's Treatise.) 

 C, second walking leg, uniramous 

 type ; cxp. bp., protopodite ; ip., 

 mp., cp., pp., dp., segments of en- 

 dopodite ; ep., epipodite. (From 

 Cambridge Natural History.) 



possesses (III) a pair of man- 

 dibles, behind which are (IV) 

 the first, and (V) the second 

 maxillae; the thoracic region 

 bears (VI) the first, (VII) the 

 second, and (VIII) the third 

 maxillipedes, (IX) the pin- 

 chers or chelipeds, and (X- 

 XIII) four other pairs of 

 walking legs; beneath the 

 abdomen are six (XIV-XIX) 

 pairs of sivimmerets, some of 

 which are much modified. 

 Table VII gives brief de- 

 scriptions of the different ap- 

 pendages, and shows the 

 modifications due to dif- 

 ferences in function. The 

 functions of some of the ap- 

 pendages are still in doubt. 



Three kinds of appendages 

 can be distinguished in the 

 adult crayfish; (i) the folia- 

 ceous, e.g. the second maxilla 

 (Fig. 102, A), (2) the bira- 

 mous, e.g. the swimmerets (Fig. 

 1 02, B), and (3) the unira- 

 mous, e.g. the walking legs 

 (Fig. 102, C). All of these 

 appendages have doubtless 

 been derived from a single 

 type, the modifications being 

 due to the functions per- 

 formed by them. The 

 biramous type probably 



