PACKARD.] MORPHOLOGY OF PHYLLOPODA. 385 
so far as my observations go. I have found them always present 
in full-grown specimens of Apus cancriformis from Munich, from Prag, 
and from Padua.” 
In spetimens of Apus cancriformis kindly sent us by Professor Sie- 
bold, of Munich, we have found the second antenne to be inserted on the 
inner declivity of the frontal doublure forming the front of the head, 
and inserted behind the first antenne, and farther out from the labrum 
than the first antenne. They are in form as described and figured by 
Lankester. I also found them in my examples of Apushimalayanus, and, 
as in A. cancriformis, they are larger and more easily found than in the 
American species. 
On looking for the second antenne in our American species I was at 
first unable to find them, they were so minute and so closely appressed to 
the body. In specimens of Lepidurus couesii which were well preserved 
the antenne were found, but nonein L. bilobatus, of which I had but two 
indifferently preserved specimens. Figs. 2b, 2c, of Plate XXXII, show 
their relative size in Apus lucasanus, both being drawn to the same 
scale. In order to find them the mandibles have to be forcibly moved 
backward. They were also found in Apus newberryi, A. equalis, and in 
A. longicaudatus, but in all these American species they are much smaller 
and more difficult to find than in the European and Asiatic species; a 
point of some interest, which coupled with the greater obsolescence of 
the maxillipedes and the smaller carapace shows that the American 
species have reached a stage farther removed from the larval condition 
than the Old World forms. 
Histology.—The histological structure of the 2d antennee of the Limna- 
diade is shown at fig. 2, Plate X XIX, which represents the three terminal 
joints of one of the flagella of the second antenne of Hstheria. The joints 
areseen to be crowded with nerves of special sense, and the antennal nerve 
is seen to terminate in fibers, one of which passes into each seta; so that 
these organs must be highly sensitive, perhaps only tactile, however, 
while they are also rowing or Swimming organs. 
The mandibles.—All Phyllopoda have well-developed mandibles, ex- 
cept in the highest or most specialized family, the Branchipodide, in 
which they are weak and feeble in function, though with primarily the 
form common to the group. 
In the Limnadiade (according to Lilljeborg), in Limnadia gigas, and as 
we have observed in the Apodida, the mandibles are without a palpus in 
the adult, and are solid chitinous appendages with the biting edge either 
smooth, as in Limnadiad@, or provided with strong acute teeth as in 
Lepidurus and Apus. (Plate XXI, figs. 11, 12.) 
When we look at the larval mandibles of Apus, which are represented 
by Dr. Gissler (Plate XXXV, fig. 1, md), it is not only plain that 
they are the third and last pair of the limbs of the Nauplius, but it is 
also plain that the mandible originally consists of two portions, the 
basal joint with its masticating edge and the two-jointed palpus; this 
palpiform appendage becomes absorbed or at any rate disappears in the 
two families under consideration, and it is easy to see that the mandible 
proper represents or is the homologue of the basal joint of the axis of 
the limb, together with the first endite, coxal lobe, or gnathobase of the 
eau Limnadiad or Apodid leg (e.9., Plate V, figs. 51, 7a; Plate XX1I, 
g. 4cl). 
In the Apodide the cutting edge of the mandible is provided with 
eight or nine teeth, which are naturally Jess blunt in the adult than in 
the larva (see Plate XXXYV, fig. 4, 4a palpus). 
In the Branchipodida the mandibles, as shown by Spangenberg (suppl. 
25 H 
