EMBRYOLOGY OF THE KING-CRAB. 301 
the serous membrane (Fig. 266, am), which is like that of 
insects. 
Then the limbs bud out; the six pairs of cephalic limbs 
appear at once as in Fig. 266. Soon after the two basal 
pairs of abdominal leaf-ike feet arise, the abdomen be- 
comes separated from the front region of the body, and 
the segments are indicated as in Fig. 26% A later stage 
(Fig. 268) is signalized by the more highly developed dorsal 
portion of the embryo, an increase in size of the abdomen, 
and the appearance of nine distinct abdominalsegments. The 
segments of the cephalo-thorax are now very clearly defined, 
as also the division between the cephalo-thorax and abdomen, 
the latter being now nearly as broad as the cephalo-thorax, 
the sides of which are not spread out as in a later stage. 
Fig. 268.—King-crab shortly before hatching ; trilobitic stage, enlarged ; side and 
dorsal view. 
At this stage the egg-shell has split asunder and dropped 
off, while the serous membrane, acting as a vicarious egg- 
shell, has increased in size to an unusual extent, several 
times exceeding its original dimensions and filled with sea- 
water, in which the embryo can freely move. 
At a little later period the embryo throws off an embry- 
onal skin (amnion), the thin pellicle floating about in the 
egg. Still later in the life of the embryo the claws are de- 
veloped, an additional rudimentary gill appears, and the 
abdomen grows broader and larger, with the segments more 
