396 GEOLOGICAL SURVEY OF THE TERRITORIES. 
in the nerves, ¢. e., forming ganglionic enlargements, while there is a 
marginal fine nerve which connects the ends of the setal nerves. The 
structure and arrangement of the nerves in the sixth endite of Estheria 
appears to be nearly the same as in the Branchipodida, described far- 
ther on, and the ganglion-cells are seen to be of the same size, the 
parts being magnified with + Tolles A eye-piece. Plate X XIX, fig. 
4, represents the end of the oviger of the same leg as fig. 7, Plate V. 
A ganglion and setal nerve supply each seta, while the main nerve 
passes through the middle, at tx, being reinforced by ganglion-cells ; 
while at the end are several cells from which a nerve passes into each 
seta. / 
In Lulimnadia texana (Plate VII, fig. 2, 2a, 2b) where the fifth endite 
of the first leg of the male is provided with a minute palpus-like pro- 
cess, which was not observed in Hstheria, the histological structure of 
the. second joint is the same, though the nerve-fibers were not so dis- 
tinct in the specimen examined; Hulimnadia differs, however, in the 
terminal setz being coarser and much more numerous. 
In the Apodida, trom the nature of the dense opaque integument of the 
appendages, it is probable that no special sense-apparatus is present. 
In the delicate swimming thoracic appendages of the Branchipodide 
some interesting histological features were observed, especially in legs 
stained with carmine. 
In Branchipus vernalis the edges of the endites are provided with 
clusters of two or three ganglion-cells which are situated in the mar- 
gin near the insertion of the sete. These are noticeable in the fifth 
endites, but especially so in the paddle-like sixth endite. (Plate XXX, 
fig. 1.) This figure is drawn with the camera lucida and shows the 
relation of the muscles supplying it, and also of the peculiar system of 
ganglionic nerve-cells and nerves supplying the marginal tactile sete. 
The striated muscular fibers are situated in the ceutral portion of the 
foot (muscle); they suddenly terminate in the manner indicated in the 
figure, and originate from a median muscle passing out of the axis of 
the limb; associated with them are irregular groups of ganglion-cells. 
The marginal ganglion-cells are arranged in two series: a submarginal 
set (nc') aud a marginal set (nc). Whether the masses of parenchy- 
matous matter filling the spaces between the two sets is truly nervous 
matter, or undifferentiated protoplasm, I cannot say, but, judging by fig. 
3, it is probably nervous. At the base of the anterior margin of the 
endite where the setz are reduced in size the submarginal series of cells 
disappear. Toward the posterior margin the setal nerves are seen to 
enter the seta from a group of submarginal ganglion-cells. The con- 
nection of the submarginal and marginal series of cells and nerves with 
@ main axial nerve of the leg was not observed, though several speci- 
mens were examined and search made for it, and hence I am inclined 
to think that the system of setal nerves and their cells is independent 
of the central nerve system. 
In fig. 2 of the same plate is represented the sixth endite of one of 
the anterior legs of Streptocephalus texanus, in which there is nearly the 
same relation of parts asin Lranchipus. The axial branches of the two 
muscles (mus) are seen to be in one case connected with the series of 
striated muszles in the central area of the endite. No main endital 
nerve was detected, and here, as in Branchipus, we see the same system 
of submarginal and marginal nerve-cells, and of setal nerves. The cells, 
however, are less numerous as seen in fig. 3, which represents the end of 
_ abundle of striated muscular fibers; also their mode of termination, the 
Space between the ends of the muscular fibers, and the submarginal 
