L obster — A natomy , Sexes. 
19 
kidneys of the Vertebrate animals) is represented by a pair of Wall- 
glands known as the “ green glands ” lying at the sides of the head g 
and opening to the exterior each on a small tubercle on the first 
segment of the antenna. 
The central nervous system consists of a “ brain,” lying in front 
of the head, connected by a pair of cords which pass on either 
side of the gullet with the “ventral nerve chain” in which may 
be distinguished twelve nerve centres or ganglia. 
The eyes, as already mentioned, are set on movable stalks. 
The black, kidney-shaped area at the end of the stalk can be seen, 
under a magnifying lens, to be divided into numerous minute 
facets (some 13,500 in number), for the most part square in 
outline. It is not correct to state, as is sometimes done, that each 
facet corresponds to a separate eye, forming a separate image of 
the object looked at ; the whole assemblage of facets and the 
structures underlying them co-operate to form a single image on 
the receptive nerve-endings in the interior of the eye. 
In the basal segment of the antennule is the so-called auditory 
organ, a small pouch open to the exterior and containing in its 
cavity a number of grains of sand. This pouch, which has on its 
inner surface numerous feathered hairs connected with a large 
nerve, was formerly regarded as the Lobster’s ear. Although it is 
not impossible that it may have to do with the sense of hearing, 
recent investigations have shown that its principal function is 
connected with maintaining the equilibrium of the body in walking 
or swimming. 
The dissection exhibited (see Fig. 4) is one of a male Lobster, 
and the testis can be seen lying below the heart and giving off a 
duct, the vas deferens, which opens to the exterior on the coxa of 
the last pair of legs.* 
Differences between the sexes.— Two preparations are 
exhibited in order to show the chief external differences between 
the sexes of the Lobster (Fig. 5). The most easily noticeable 
differences are the greater breadth of the abdomen and the larger 
size of its side-plates in the female than the male. The first pair 
of swimmerets (which, unlike the other pairs have only one branch 
in both sexes) are very slender in the female, but are much larger 
and peculiarly shaped in the male. The second pair have an 
additional lobe on the inner side of the endopodite in the male. 
The openings of the genital ducts can be seen on the first segment 
(coxa) of the last pair of walking legs in the male, and on that of 
the last pair but two in the female. Finally, the female has on 
c 2 
