382 GEOLOGICAL SURVEY OF THE TERRITORIES. 
first antennal segment; and, as it is a general law that but a single 
pair of appendages are borne by a single segment, we should not expect. 
to find the law broken in this case, at least as regards the cephalic seg- 
ments. 
When we come to the Branchipodide, where the eye is mounted on a 
long moveable stalk, they are still plainly tergal outgrowths of an an- 
tennal segment. The embryological history of the eyes would also prove 
that the eyes in all stalked Crustacea first begin as a specialized group 
of epidermal cells, developing on the anterior segment of the head; even 
in the zoéa of Decapods, the eyes remain sessile until just before the 
hatching of the larva; the growth of the stalk is one of the latest 
changes in embryonic life. If the eye-stalk were homologous in its his- 
tory and structure with the limbs, then why should not the stalk in the 
stalk-eyed species bud out from an independent primitive segment, as 
do the appendages of the cephalothorax and abdomen? Instead of that, 
the stalks on which the eyes are situated are developed very late in em- 
bryonic life, and are evidently not derived from ancestral forms; while 
in all stalk-eyed forms, whether Phyllopoda, Phyllocarida, or Decapoda, 
the stalk is preeminently an adaptive feature of the head, and is de- 
veloped on the first antennal segment. 
The first antenne.—The Phyllopoda have, with the. exception of in- 
dividual Apodide, invariably two pairs of antenne. They are, however, 
very unequally developed, the first pair being minute and smaller than 
the second pair, except in Apodidw, where the second pair are minute 
and sometimes wanting. In Limnetis they are minute and difficult to 
find. Their position and size in relation to the first pair are well shown 
by Mr. Burgess in Fig. 4 (in text). They are there seen to be inserted 
quite in advance of the second pair, and to be slender and two-jointed. 
Those of L. gouldi are much slenderer than in L. brevifrons. 
In Hstheria and Limnadia they are much larger and longer, multiar- 
ticulate, the joints, however, not well defined on the inner edge; they 
appear to be inserted behind the second pair, but careful examination 
shows that they originate anteriorly. In the Apodide the first antenne 
are much larger than the second pair, but small as they are, and appar- 
ently almost functionless, they are yet invariably present. The relative 
size and form of the two pairs are shown on Plate XXXII, figs. 2a, 2b. 
The first pair are inserted on the vertical inner wall of the frontal doublure. 
Thev are slender, two-jointed, and by their position and diminutive size 
must be nearly useless to the animal, and only the survival of larval 
organs. In the Branchipodide the first antenne resume somewhat of 
their normal size and importance, being rather long, slender, filamental 
appendages, but not jointed. The histology of the first antennee in Lim- 
netis has not been previously noticed. Under a high power, these of 
Limnetis gouldii (Plate X XVI. figs. 4, 4a*) are seen to be provided along 
the outer edge with long, slender sense-filaments, rather more closely 
crowded and better developed at the end than along the side. The sub- 
stance of the joint is rich in,cells which are not closely crowded, and are 
arranged in series ending at the base of the sense-filaments, where the 
cells become more closely crowded. These cells occur at the base of the 
sense-filaments, but elsewhere in the filament there are only minute scat- 
tered corpuscles of the size of the nuclei of the sense-cell. In ZL. brevi- 
frons (figs. 5, 5a) the histological structure is nearly the same, but the 
*In Fig. 4, which represents the second joint of the antenna, the left side has been 
omitted by theartist. The line which should have been drawn here has wrongly been 
added to the right side of fig.-4a. 
