38 A HISTORY OF RECENT CRUSTACEA 
Spence Bate suggests that its function may consist in p1o- 
tecting and keeping clean the mass of cilia and filaments 
attached to the outer branch. In some genera of the 
Macrura, for example Palemon and Alpheus, the principal 
flagellum divides at some distance from its base into two 
branches. In the Squillidge, also, there are three flagella. 
3. The third segment carries the outer, under, or second 
antennz, sometimes called simply the antennee in distinc- 
tion from ‘antennules.’ They are rarely absent, as in the 
females of some Amphipoda. More often they are strongly 
developed, in some instances exceeding in length all the 
rest of the animal which carries them, the joints of the 
flagellum or lash being then very numerous. In the 
Malacostraca the peduncular portion embraces the first 
five joints. The exopod, when developed, as it gene- 
rally is in the Macrura, very commonly has the form 
of a thin plate known as the antennal scale, in Latin 
squama, While those who love long words are privileged to 
call it the scaphocerite. When laterally extended this 
broad scale must assist in keeping the animal upright in 
the water, a position which would otherwise with difficulty 
be maintained by long-bodied forms. In some Crustacea, 
the scale, though present, has not a laminar character, 
and it is then spoken of as the acicle. The first, or basal 
joint of the peduncle, is not unfrequently soldered to the 
wall of the head, and very often carries a tubercle in con- 
nection with the ‘green gland,’ of which the function is 
supposed to be renal, though it has not been with certainty 
determined. That this tubercle is of some importance 
may be inferred from the fact that in some cases where 
the antenna itself is obsolete the tubercle persists. 
It is not a little singular that up to thirty years ago 
or later, many naturalists of eminence regarded this tuber- 
cle as connected with the auditory apparatus, which they 
assigned to the base not of the first but of the second 
antennee. Milne-Edwards in 1834 refers to the researches 
of M. Savart, who had discovered that the stretching of a 
fine elastic membrane over an opening was one of the 
circumstances best adapted to promote the appreciation of 
