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O14 7 SCIENCE. 
swimming-organ. It is much broader than the rest 
of the abdomen, and is used as a paddle to augment 
the effects of the powerful strokes of the abdomen. 
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Fig. 1.— Protozoea of Lucifer (after Brooks). Fic. 2.— Zoea 
of Gebixi. Fia.3.— Zoea of Panopeus. Fre. 4.—Telson of 
Panopeus zoea. 
It still retains a number of spines, but they are usu- 
ally quite small. 
A third type is the zoea of the ordinary crab. Fig. 
[Vou. Ill., No. 64. — 
3 is such a zoea. Here we see a number of striking 
peculiarities. As in the shrimp zoea, we find no 
middle body; i.e., the thorax is absent. The abdo- 
men is quite small, and always occupies a character- 
istic position. Instead of being stretched out behind 
the body, as in the shrimp zoea, it is bent under the 
cephalothorax, as in the figure. Still another mode 
of locomotion is herefound. It is true that occasion- 
ally it uses its tail; but its ordinary locomotion is 
neither with antennae nor abdomen, but by means of 
its first two pairs of maxillipeds. These are very long, 
and carry large numbers of swimming-hairs, and serve 
as oars, with which the zoea paddles itself along. Its 
motion, while swifter than that of the protozoea, is not 
so vigorous as that of the shrimp. The tail has be- 
come modified into a form halfway between the tails 
of the other two larvae described. It is somewhat 
broadened, and probably has a slight motor function; 
but its chief use is protection (fig. 4). The most 
noticeable feature is the very remarkable cephalotho- 
rax. This is of enormous comparative size, entirely 
covering the body when the abdomen is flexed. It is 
further armed with a number (usually four) of long 
spines, which project in different directions, and are 
strong and sharp. No one can be in doubt as to the 
use of this arrangement. The large cephalothorax, 
with its resisting spines, serves as a protective case for 
the more delicate organs within; and, further, when 
the abdomen is flexed, the spines of the peculiar tel- 
son are placed in such a position as to give additional 
protection, being then directed forwards. 
Now, is there any connection between these three 
forms, and is it possible to discover any explanation 
for their peculiarities? In the first place, comparative 
embryology shows good reasons for believing that the 
first type, protozoea, is the oldest, and that the others 
are derived from this form. The evidence cannot be 
here deduced, but may be found by referring to Claus, 
Brooks, or Balfour. Assuming, then, this to be the 
case, the question resolves itself into the simpler one, 
what caused the protozoea to undergo changes which 
converted it into the remarkable zoea form ? 
A simple experiment, easily performed by any one 
at the seashore, suggests ananswer. ‘The experiment 
is simply to endeavor to catch a specimen of each of 
these types of larvae with a moderately small dipping- 
tube. It will be noticed that all of the larvae seem to 
have a dread of the suction which is produced by the 
tube; and all will swim away from it, unless it be too 
strong. It will be further seen that it is next to im- 
possible to catch the shrimp zoea. He darts away 
with the vigorous strokes of his tail, and, unless the 
fisherman is very quick, he is gone. Some of the crab 
zoeas Will be easily caught; but they will be seen, upon 
examination, to have doubled themselves up into as 
compact a mass as possible, with all their spines pro- 
jecting, and consequently in position to offer the 
greatest defence against enemies. Other crab zoeas 
will be found not so easily caught. If the zoea fished 
for be of the species figured, or, still better, be the 
larva of Porcellana, and the dipping-tube be small, — 
it will be found impossible to catch it. The long — 
spines project so far in different directions, that the — 
