THE CARCINUS MASHAS. 
455 
robust. The long legs on the pereion cease to be used as swim- 
ming legs ; the pereipoda are more fully developed, and assist in 
their proper capacity ; and the pleon has lost its forked extremity. 
The antennae scarcely differ from those of the adult, and the 
olfactory organ is present in an immature form. The true swim- 
ming legs, or pleopoda, have branches and hairs, and have become 
useful organs, and the telson has lost its appendages. Some other 
moults deprive the animal of the spine on the back (dorsal), the 
carapace becomes much altered in shape, especially near the eyes ; 
the auditory organ has become further developed ; the walking legs 
have increased in size, and the claws also. 
When the young crab becomes a little larger, though still of the 
same form, the segments of the pleon in the male commence a 
a fusion together. The eyes are prominent, and resemble more 
and morq^those of the adult stage ; but the most striking altera- 
tion is the gradual extension of the carapace behind the eyes. 
The telson gradually assumes the shape of a blunt point fringed 
with hairs. 
Gradually the successive moultings are accompanied by the 
approach to the adult form, and this is finally reached, evidently, 
without any distinct stage of quiescence. 
Mr. Spence Bate sums up the result of his observations as 
follows : — “ In contemplating the development of the decapod 
Crustacea , from the youngest and most anomalous form to that of 
the adult, we perceive that the greatest amount of change, both in 
appearance and the development of parts, takes place in the 
Brachyura ; but that even here the change is no sudden trans- 
formation of one form into another, but a gradual and persistent 
growth following each successive moult. Every part that is 
present in the larva, though not permanent in itself, is to be 
found in a permanent condition in one or other form of adult 
Crustacea ; and, moreover, those appendages which play the most 
important parts in the larva fulfil only secondary conditions in 
relation to the adult. Thus the large natatory limbs in the larva 
become the palps of the adult Gnathiopoda , and the appendages of 
the second antennae either represent unimportant parts of the same 
organ or are altogether wanting. Again, we perceive that certain 
parts which contiune present with but a small amount of alteration, 
