I APPENDAGES 9 
We may dismiss the uniramous type with a few words: it 
is obviously secondarily derived from the biramous type; this 
can be proved in detail in nearly every case. Thus, the uniramous 
second antennae of some adult forms are during the Nauplius 
stage invariably biramous, a condition which is retained in the 
adult Cladocera. Similarly the uniramous walking legs of many 
Decapoda pass through a biramous stage during development, 
the outer branches or exopodites of the limbs being suppressed 
subsequently, while the primitively biramous condition of the 
thoracic limbs is retained in the adults of the Schizopoda, which 
doubtless own a common ancestry with the Decapoda. The only 
Crustacean limb which appears to be constantly uniramous both 
in larval and adult life is the first pair of antennae. 
We are reduced, therefore, to two types—the foliaceous and 
biramous. Sir E. Ray Lankester,’ in one of his‘most incisive 
morphological essays, has explained how these two types are 
really fundamentally the same. He compares, for instance, the 
foliaceous first maxillipede (Fig. 1, A), or the second maxilla 
(Fig. 1, B) of a Decapod, e.g. Astacus, with the foliaceous thoracic 
linb of Branchipus (Fig. 1, D), and with the typically biramous 
first maxillipede of a Schizopod (Fig. 1, F). 
In each case there is present, on the outer edge of the limb, 
one or more projections or epipodites which are generally 
specialised for respiratory purposes, and may carry the gills. 
The 6th and 5th “endites” in the foliaceous limb (Fig. 1, D) 
are compared with the exopodite and endopodite respectively 
of the biramous limb, while the endites 4-1 of the foliaceous 
limb are found in .the basal joints of the biramous limb. 
Lankester presumes that the biramous type of limb throughout 
has been derived from the foliaceous type by the suppression 
of the endites 1-4, as discrete rami, and the exaggerated 
development of the endites 5 and 6, as above indicated. 
The essential fact that the two types of limb are built on the 
same plan may be considered as established; but it may be 
urged that the biramous type represents this common plan more 
nearly than the foliaceous. It is, at any rate, certain that in 
the maxillipedes of the Decapoda we witness the conversion 
of the biramous type into the foliaceous by the expansion of 
the basal joints concomitantly with the assumption by the 
t Quart. J. Micr. Sct. xxi., 1881, p. 343. 
