350 
POPFLAE SCIENCE EEVIEW. 
however, is the scaphognathite, or hoat-like Jaw, on each side, 
which continually spoons out the water from the gill-chamber in 
front, and thereby causes a current to enter from behind. 
The nervous system consists of a longitudinally-disposed series 
of different sized ganglia, connected together by commissural 
cords, and placed in the ventral region of the body. 
Primitively there is a pair of ganglia to each somite, but the 
three first pairs fuse, in the adult, into a large cerebral ganglion 
placed in front of the mouth, and called the brain. From this 
a nervous cord passes back on each side of the gullet to the large 
post-oral ganglia, which is made up of six pairs of primitive 
ganglia fused together. Then follow five pairs of thoracic and 
six abdominal ganglia, all distinct, but connected one with 
another by a nervous band formed of the primitive commissural 
cords which have coalesced in the middle line. 
No solid internal skeleton separates this nervous axis from the 
alimentary system, though reflections of the external integument 
(apodemata) pass inwards and more or less protect it. From 
this nervous axis all the nerves are given off, but none arise by 
two distinct roots like the spinal nerves of man. 
The organs of sense known are but two, as no organ of smell 
has been determined, and the functions of the antennae and 
antennules can only be speculated about. They are probably 
tactile organs, but of course may be the seat of senses to us 
unknown and inconceivable. 
The two eyes are compound ones — that is to say, each has its 
surface divided into a great number of quadrangular facets, which 
are the external boundaries of conical club-shaped bodies sepa- 
rated from each other by pigment and connected with the optic 
nerve. The true nature of this eye is not yet determined, but 
it may probably turn out to have a very remarkable resemblance 
to that of the human retina.* 
The ear is situated in the protopodite of each antennule, and 
consists of a small sac opening ' externally by a narrow cleft 
guarded by hairs. At the bottom of the sac is a prominence 
wherein the auditory nerve terminates, and on which are very 
delicate hairs with siliceous particles which have found their 
way in from the exterior. 
A green gland exists at the base of each antenna, and com- 
municates with a sac which opens externally on the protopodite 
of that appendage. This gland is said to be the kidney of the 
lobster. 
Each individual is either male or female, and the latter may 
be distinguished by its deeper pleura and more hairy swim- 
* This was pointed out by Professor Huxley in his Hunterian Course 
for 1868 . 
