’ HOMOLOGIES OF THE CRUSTACEAN LIMB. 407 
while the endopodite and exopodite of the Decapoda represent the en- 
dopodal portion of the limb of the lower groups. There is in the Phyl- 
lopoda no division into a coxopodite and basipodite or stalk, from 
which two axially jointed divisions branch off, homologous with the 
exopodite and endopodite of the Decapoda. In the latter the max- 
ip eae 
gil 
cacp 
Fic. 33.8, third maxiilipede; erp, coxopodite; bp, basipodite; ip, ischiopodite; mp, meropodite; 
Berean: pp, propodite; dp, dactylopodite; c, multiarticulate extremity of exopodite or palpus; 
ab, epipodite. 
Norr.—The maxilla and maxillipedes of the lobster are drawn in their natural position; so far as 
possible the exopodai portion (gill and flabellum) dorsal, and the endopoda! portion ventral to compare 
with the Phyllopod limbs. (Compare Plates xxiv and xxxii and Fig. 34. Apus.) 
illipede is highly differentiated; in the thoracie limbs of the Phyllo- 
carida and Merostomata it is uniaxial and jointed, but in the Phyl- 
lopoda not truly jointed. In the simplest Decapod limb, that of 
the abdomen, we have a stem succeeded by two divisions, the exopodite 
and endopodite; in the theracic feet we have but one of these branches, 
the endopodite, whilein the maxillipedes, the most differentiated, we again 
have a stem and two branches (endopedite and exopodite), together with 
the gill and flabellum. Thus the entire leg of the Phyllopod (without 
the gill and flabellum) is homologous with the endopodite of the Deca- 
pod maxillipede, and the gill and flabellum with those of the Decapoda. 
Comparison with the thoracic limbs of Nebalia (Phylocarida).—Not to 
enter into detail, by a glance at the accompanying figure (36) and the fig- 
ures in Plate XX XVII, as well as the wood-cuts in section VII, it will 
be seen that the thoracic appendages of Nebalia consist of an inner 
axial, jointed portion (the endopodite), which may perhaps be regarded 
as homologous with the endopodite of the Decapod maxillipede, and also 
with the thoracic legs of the lobster. This also corresponds to the en- 
dopodal unjointed portion of the Phyllopod thoracic limb. In the exo- 
podal or respiratory portion (ex) the upper part corresponds to the Phyl- 
lopod gill, and the double lower portion to the flabellum. 
Comparison with the feet of Limulus (Merostomata).—The resemblance 
between the abdominal legs of Limulus and the thoracic ones of Nebalia 
is apparent on inspection of figs. 36 aud 57 (p. 409). In Limulus the shell 
flares out widely and the appendages are united in the middle, although 
separate in embryonic life, so that this is a feature of secondary import- 
ance. The point of special interest is that the abdominal feet of Limulus 
may, asin the thoracic appendages of the Phyllopoda and of the Phylloca- 
rida, or the maxille, maxillipedes, and thoracic feet of the Decapoda, be di- 
vided into an inner endopodal portion (whetber ambulatory or natatory), 
