208 MR. LUBBOCK ON SOME FRESHWATER ENTOMOSTRACA. 
female, is about one-third shorter. So far as my observations at present go, this 
is not the case in ZL. productus. As I have just mentioned, of my largest speci- 
mens the great majority were males; on the other hand, it must be admitted that 
none of them were more than, or even quite so much as an inch and three quarters in 
length, and, as the species is stated to attain a length of two inches and a half, it is still 
possible that the full-grown females may be considerably larger than the males. 
-Homologies.—'* The Phyllopoda ” (says Prof. Dana) “in which the number of segments 
exceeds the normal number, offer a difficult problem to science, viz. the determination 
of the normal relations of the appendages. In Branchipus the number of segments is 
twenty-two, of which nine belong to the abdomen, eleven to the body posterior to the 
second pair of maxille, seven being the normal number for the former, and eight for 
the latter. In Limnodia there are eighteen or twenty-seven pairs of thoracic members 
following a pair of maxillze and mandibles. In Apus there is a pair of mandibles, then 
two of maxille, then a large series of legs, all of which are more or less foliaceous, 
excepting the anterior. In Nebalia the abnormal character is the same, although their 
members are not as much multiplied."  . 
And he offers the following explanation of the difficulty :— 
“The most natural supposition,” he says, “in view of the fact that the members of 
Crustacea consist normally of three parts or branches, a tigellus, a palpus, and a fouet, 
is that the multiplication consists in these several parts (two of them or the three) 
becoming separate legs, and at the same time having separate segments in the body, the 
normal basal portions of each possibly corresponding to these segments; and possibly 
we see some analogy also in the multiplication of branchisz, two or three being often 
appended to a single leg, in the Decapods." | 
Notwithstanding the ingenuity of this idea and the great weight of Prof. Dana's 
authority, I cannot bring myself to adopt this hypothesis. If we examine the relation 
which the legs bear to the segments, we shall find that the anterior eleven legs are each 
attached to a separate and well-marked somite. "Though the position of the posterior 
appendages as regards their relation to the segments is not quite so easy to determine, 
still a glance at the animal will show that the size of the dorsal arches does not decrease 
in proportion to that of the legs; so that while the twelfth segment has only a single 
pair, the number gradually increases until we find that the last nine pairs correspond 
to a single dorsal segment. 
But it is evident that these legs are all homologous. Much as the extremes differ from 
one another, they are connected together by so gradual a series that no one who has 
examined them can have any doubt on this point. There is, indeed, one apparent 
exception, namely, the eleventh pair in the females; but this is evidently modified for 
a special purpose, and the corresponding pair in the males is, as we have seen, of the 
usual form. Moreover, even if we were to admit (for which, however, we have not the 
slightest reason, and which would indeed be entirely contrary to all evidence and 
experience) that this pair is of a different nature to the rest, still it would not be any 
support to Prof. Dana's hypothesis. Nor can it, I think, be maintained that the sternal 
segments do not really belong to the dorsal arches with which they appear to correspond ; 
