PACKAED.] MOEPHOLOGY OF PHYLLOPODA. 391 



The axis of the second pair of bsenopods is composed of two joints, 

 but we should not agree with Laukester's notation of the joints ; the 

 joint marked 1 includes what corresponds to ax^ and ax^ of the first leg ; 

 and his joint 2 {ax^) corresponds to ax^ and ax* of the first leg ; in other 

 words, of the two divisions of the axis of the second leg the first repre- 

 sents the two basal joints of the first leg and the second the third and 

 fourth. So it seems to us the "joints" are more or less arbitrary sub- 

 divisions of the axis, and are not, properly speaking, true joints, hence 

 we would call them pseudo-joints or subjoints. 



Begianing with the endites, the first is transformed into a large, broad, 

 thick, squarish lobe, whose inner edge is beset with dense fine, stifi" sette. 

 This is the gnathobase of Lankester, and what we have called the coxal 

 lobe (Plate XIX, fig. 3, elsewhere c/, or l^). The gnathobase of each limb 

 is diverted outward and backward, and thus, with those of the oiher 

 limbs, forms a long series bordering the median sternal line of the body 

 behind the mouth-parts, and which, as in the Limnadiadcc, serves to re- 

 tain the food and to push it toward the mouth and jaws. 

 . We should not, as Professor Lankester appears to do, say that " a 

 similar feature is characteristic of Limulus." The set of stiff spines in 

 tlie Merostomata are developed directly upon the coxopodite or ba^ai 

 joint of the limb, which is directly homologous with the coxopodite of a 

 crab, the resemblance to that of Apus is one only of analogy, though a 

 very interesting one ; the function, of course, being the same in each. 



The succeeding five endites of the first pair of limbs are similar i-n. 

 form, being subjointed, the joints not, however, being complete and not 

 movable upon each other, the sutures marking them only extending 

 part way towards the middle of the process. The third, fourth, and 

 fifth endites, particularly the fifth, are remarkably long and autenni- 

 f(>rm. The sixth forms a minute pointed scale, whose base is confluent 

 with that of the fifth. 



The gill in the Apodida? is rather small and pyriform ; while the fla- 

 bellum is very simple in form compared with the Liinnadiadce, but still 

 well provided Avith muscles, and, as in the latter family, forming the 

 I)rincipal swimming as well as respiratory organs. They are triangular, 

 the outer end rounded, the inner pointed and somewhat produced, but 

 there is no such interesting differentiation in form and function as occurs 

 in the Limnadiad flabellum. 



Both exites and endites are remarkably persistent in form in the dif- 

 ferent species and are not of much use in taxonomy. 



In the larva, 2 J™"" long, of Apus lucasanus, as drawn by Gissler (Plate 

 XXXV, fig. 7), which corresponds well with (Jlaus's drawing of the 

 same stage in Ajnis cancriformis I have added the references to the 

 pseudo-joints {ax^-ax^). The gnathobase has two series of spines, the inner 

 short ; the sixth endopodite is seen to be very long and slender, while 

 it is minute, short, and broad in the adult. The two spines at the end 

 are noticeable, as there are four small ones in Claus's drawing. The 

 flabellum is very much smaller than in the adult, while the gill is but 

 little larger. 



podite, and epipodite, supported on a protopodite or basal division (fig. 63 D, E. F). 

 The latter consists of three joints — a coxopodite produced internally into a strongly 

 setose prominence (not ref)resented in the figures), a basipodite, and au ischiopodite, 

 the latter elongated internally into a lauceglate process, and bearing on its outer 

 side two appendages, of which the proximal — the epipodite or branchia is pyriform 

 and vesicular in specimens preserved in spirits. The distal appendage which appears 

 to represent the exopodite (G) is a large flat plate, provided with long setse on ita 

 margin." Huxley did not find the maxillipedes and second antenusB in Lepidurus 

 glacialis. 



