134! ELEMENTARY ElOLOGT. [xit 



the young, when hatched, are larv^ extremely unlike the 

 parent, which undergo a series of metamorphoses in order 

 to attain their adult condition. The larvae may frequently 

 be obtained by opening the eggs of a 'hen-lobster' in 'berry.' 

 They have a rounded carapace, two large eyes, a jointed 

 abdomen devoid of appendages ; and the thoracic limbs are 

 provided with long exopodites. 



The ordinary growth, no less than the metamorphoses 

 of the Lobster and Crayfish, are accompanied by periodical 

 castings of the outer, chitinous, layer of the integument. 

 After each such ecdysis, the body is soft and the animal re- 

 tires into shelter until the 'shell' is reproduced. 



LABORATORY WORK. 



1. General external characters. 



The animal is covered by a dense exosJceleton : in it 

 are readily recognised the following parts : — 



a. The body proper : 



a. Its anterior unsegmented portion {cephalotho- 

 rax): the great shield-like plate {carapace) 

 covering the back and sides of the cephalotho- 

 rax; the groove across the carapace (cervical 

 suture) marking out the line of junction of 

 head proper and thorax: the anterior prolonga- 

 tion of the carapace to form the frontal spine. 



/3. The posterior segmented portion {abdomen) : 

 its seven divisions; the anterior six much like 

 one another; the most posterior {telson) different 

 from the rest. 



