93 . REPORT — 1876. 



Mysis a very similar appendage is the 'basecptj-sis, while the bfanchise ard, 

 in all cases when present, the homologaics of the coxecphj-sis. 



The next five succeeding pairs of appendages are the true legs as they 

 exist in the typical forms of Crustacea, and it is from the general appearance 

 of them that the higher forms are known as Decapoda, or Ten-footed Crus- 

 tacea. In a scientific point of view the name is incorrect and misleading ; 

 for in manj^ of the Macrura and the Edi-ioplithalmia they are twelve or 

 fovirteen in number, while in the Anomura the departure of the last two 

 pairs of pcrciopoda from the tjpical form is as great as the two first in 

 many other forms ; consequently the name of Decapoda, as well as Dana's 

 name of TetracUcapoda, is both incorrect and homologically untrue. These 

 five pairs constitute the tenth to the fourteenth pairs of appendages ; but as 

 they are limbs attached to the pereion, I have elsewhere suggested that they 

 should bo known as pereiopoda. Milne-Edwards, in his nomenclature, has 

 not identified them with any distinguishing name ; he merely calls the anterior 

 pair, which is cheliform in many genera, by the name of bras (arms), and the 

 lestjyattes (feet), and it is remarkable that he should identify each one of the 

 seven joints that is present in its construction by a distinguishing term ; but 

 the entire member he defines by an imscientific but popular phrase that is 

 inconvenient, as it is found that the prehensile power is not confined to a 

 single pair, but, as in Asfacus and Homarus, is the property of other limbs, 

 while in some, as in Sc)/UarHS, it does not exist in any. Carrying this 

 observation into other forms, we find that in certain Amphipoda the great 

 chelate or arm-like organ exists in the fifth pair of pereiopoda, as in 

 Phronima. Thus we see that the power of being developed into a grasping 

 forceps or hand exists in each or all the pereiopoda in succession ; therefore 

 the term of arm, or bras, is inadmissible in a scientific nomenclature. I there- 

 fore propose to call these five pairs of appendages the pereiopoda, in accordance 

 with the terms used in the ' History of the British Sessile-ej-ed Crustacea.' 



They invariably consist of seven joints ; these are most distinguishable in 

 the Macrura and the lower forms. In the Report on the Sessile-eyed 

 Crustacea, 1855, the author clearly demonstrated the several joints respec- 

 tively in the Amphipoda. This required no effoi't on his part to interpret 

 in the Macrura, since in Homariis, Astaciis, and Pcdinurus the general 

 points are very distinguishable ; but as we examine higher in the scale of 

 animals, we find that in the Anomura the coxce of the several pairs of legs 

 are gradually becoming absorbed and becoming part of the ventral surface 

 of the body ; and this in the Brachyura is earned still further, inasmuch as 

 it is difficult to define how much of the structure is due to the legs and how 

 much to the body, and it is not improbable that the appendages have en- 

 croached upon and absorbed the generallj' more important structure. 



The coxa or first joint appears to be essential to the existence of the animal, 

 inasmuch as it is the seat of all the more important organs connected with 

 the vital existence. The auditory and olfactory senses are situated in the 

 cosas of the antenna?, and all the branchial appendages have their origin in 

 the coxfe of the pereiopoda, while the sexual organs, both male and female, 

 are implanted in the coxfc of the seventh and fifth pairs respectively. The 

 next two joints of the limbs may, and in some of the Stomapoda do, carry 

 appendages attached to them ; but none of the joints beyond the ischium are 

 ever so furnished. 



The anterior pair is the one most commonly developed in the higher forms 

 into large chelae or hands. It is the more general in the male than in the 

 female, and I have commonly observed that the female chela generally 

 corresponds more closely with the less-developed chela in males than with 



