THE CARCINUS M^NAS. .. 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 more 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 

 BracJiyura ; 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 continue present with but a small amount of alteration. 



