38 A HISTOEY OF EECENT CEUSTACEA 



Spence Bate sugge&ts that its function may consist in pio- 

 tecting and keeping clean the mass of cilia and filaments 

 attached to the outer branch. In some genera of the 

 Macrura, for example Palcemon and Alpheus, the principal 

 flagellum divides at some distance from its base into two 

 branches. In the Squillidse, also, there are three flagella, 



3. The third segment carries the outer, under, or second 

 antennae, sometimes called simply the antennae 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, vs^hen 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 the antenna itself is obsolete the tubercle persists.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 

 autennse. 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 



