HOMOLOGIES OF THE CRUSTACEAN LIMB. 



407 



while tlie 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- 



FiG. S3. — B, third maxillipedei ccrp, coxoporlite; hp, basipodite; ip, ischiopodite ; '>np, meropodite; 

 cp, cari)opodite; 'pp, propodite; d^, dactylopodite ; c, inultiaiticulate extremity of exopodite or palpus; 

 fiab, ('pipodite. 



Note. — ThemaxillfB aad maxiTlipedes of the lobster are drawn in their natural position; so far as 

 possible the exopodal portion (sill and flabellura) dor.sal, and the endopodal portion ventral to compare 

 witli the Phyllopod limbs. (Compare Plates xxiv and xxxii and Fig. 34. Apus.) 



illipede is highly differentiated; in the thoracic 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 thoracic feet we have but one of these branches, 

 the endopodite, while in the maxillipedes, the most differentiated, we again 

 have a stem and two branches (endopodite 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 thordcic limbs of Nebalia (Phyllocarida). — Not to 

 enter into detail, by a glance at the accompanying figure (30) and the fig- 

 ures in Plate XXXVII, 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 i^art corresponds to the Phyl- 

 lopod gill, and the double lower j^ortion to the flabellum. 



Gomparisonicith the feet of Limulus (Merostomata). — The resemblance 

 between the abdominal legs of Limulus and the thoracic ones of Xebaiia 

 is apparent on inspection of figs. 36 and 37 (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, as in the thoracic appendages of the Phyllopoda and of the Fhylloca- 

 r^^a, or the maxillsB, maxillipedes, and thoracic feet of the Decapoda, be di- 

 vided into an inner endopodal portion (whether ambulatory or natatory), 



