390 GEOLOGICAL SURVEY OF THE TERRITORIES. 
Apus as the axis or corm; and finds that the first and second pairs only 
are divided into joimts—the first pair into four joints, and the second 
into two joints; the remaining pairs not being jointed. The figures in 
our Plates X VII-XX were drawn chiefly to exhibit the zoological differ- 
ences of the appendages in our American Apodide without reference to 
| the morphology of the axis, but Ret 
since reading Professor Lankes- i 
| ter’s suggestive paper we havere- 
| exantined the appendages; and 
our observations teach us that, 
‘as he states, only the first and 
second pair of feet show traces 
of joints, and even these are such 
as to be easily overlooked, and 
should rather be styled pseudo- 
joints (or pseudarthra). Plate 
_ XXXI, fig. 4, shows the pseudo- 
segmentation of the axis of the 
first pair of feet in Apus lucasa- 
NUS. 
As our figure indicates, the 
basal pseudo-joint (az') bears the 
first endite or gnathobase; the 
second pseudo-joint (ax’) is in our 
- OS Fic. 26.—Section of Apus. At. heart; tnt, intestine; 
species reduced to a minimum, ng, ganglion; ¢. carapace; 1-6, the six ’exites, 1 being 
but the second endite rises from the cnathobase ; gill and fo. flabellum, representing the 
ites. Partl di 2 ti 
it; this joint is represented by °* ~*y S@smman’ 
Lankester as being much larger in the European species. The third 
‘ joint is tolerably well marked, but its basal limits are not differen- 
tiated well from the outer part of the first joint. The third endite 
is thrown off by the third joint (ax?) plainly enough. The fourth joint 
(ax) is a definite segment, and from it originate the fourth, fifth, and 
sixth endites. In A. lucasanus, however, the gill and flagellum plainly 
arise from the fourth joint; but according to Lankester’s drawing of 
the same limb in A. cancriformis, these exites arise from the third 
joint. Taking into account, then, the incomplete nature of the two 
basal joints, and the fact that the succeeding pairs of feet are not jointed, 
we see that they share the nature of the feet in other Phyllopods, and 
that it is one of the characteristics of the Branchiopods in general, in- 
cluding the Phyllopoda, not to have truly jointed feet comparable with 
those of Copepods on the one hand or Malacostracous Crustacea on the 
other hand. On this account, while it may be safe to regard the basal 
joint of the anterior foot of Apus as perhaps the homologue of the 
coxopodite of Decapoda, we should not venture to go farther and homo- 
logize the succeeding more or less perfected joints with those of the 
adult Decapodous foot.* 
But the jointed nature of the first foot of Apus and Lepidurus is valu- 
able from a morphological point of view, as indicating that the endites 
are processes from the subjoints, as we may call the imperfectly difter- 
entiated joints, and do notin any Phyilopod form the joints themselves. 
* Huxley’s (Manual of the Anatomy of Invertebrated Animals, 1877) account of the 
nature and homologies of the foot of Lepidurus glacialis is somewhat inaccurate and 
misleading. He has torn away the feet represented in his fig. 63 E, F, from the body, 
leaving the gnathobase attached to the body; and this important and easily recog- 
‘nized parti is not drawn; he figures five endites but counts them backwards, beginning 
with the sixth one. The enathobase he briefly describes under the name ‘of COXOpO- 
dite. ‘‘Hach appendage, The says, ‘‘ consists of three divisions—an endopodite, exo- 
