244 THE ANATOMY OF INVERTEBKATED ANIMALS. 



tirely cephalic, as Milne-Edwards considers, is a point upon 

 which I have been able to come to no very clear determina- 

 tion ; indeed, it is a question rather for the embryologist than 

 the anatomist. 



Of the twenty pedigerous segments, the first eleven have 

 each one pair of appendages ; but, behind the eleventh, each 

 segment gives attachment to a gradually increasing number 

 of limbs, so that the twentieth carries five or six pairs. Alto- 

 gether twenty-eight pairs of appendages are attached to these 

 nine posterior thoracic segments ; these, added to the eleven 

 preceding, make thirty-nine appendages in all. While each 

 of the anterior eleven segments must be regarded as single 

 somites, the nature of the posterior ones is open to doubt ; 

 they may be single terga, the sterna and appendages of which 

 have multiplied; or, more probably, they each represent a 

 number of coalesced terga. 



Each appendage consists of three divisions — an endopo- 

 dite, exopodite, and epipodite, supported on a protopodite 

 or basal division (Fig. 63, D, E, E). The latter consists of 

 three joints — a coxopodite produced internally into a strongly 

 setose prominence (not represented in the figures), a basi- 

 podite, and an ischiopodite, the latter elongated internally 

 into a lanceolate process, and bearing on its outer side two 

 appendages, of which the proximal — the epipodite or branchia 

 (Fig. 63, D, E, 7) — is pyriform and vesicular in specimens 

 preserved in spirit. The distal appendage, which appears to 

 represent the exopodite (6), is a large flat plate, provided 

 with long setae on its margin. 



The endopodite consists of four joints, the two proximal 

 ones being much the longer, and, like the penultimate, giving 

 off internally a long process. Finally, the terminal joint is 

 claw-like and serrated on its concave edge. 



The average form of these appendages is represented by 

 (E), taken from the middle of the series; anteriorly the limbs 

 become more slender and leg-like (D)', posteriorly, on the 

 other hand, theyuire completely foliaceous, as (E) ; but the 

 same elements are recognizable throughout. 



The eleventh pair of appendages alone depart, in any im- 

 portant respect, from the rest of the series, each of these 

 being modified so as to serve as a receptacle for the ova. 

 To this end the joints of the endopodite are greatly ex- 

 panded, and converted into a hemispherical bowl ; the exo- 

 podite, metamorphosed into another such bowl, shuts down 

 over the endopodite ; and into the box thus formed the 



