28 



Nauplius, three pairs of appendages. 



Protozoea, more than three pairs but not more than eight 

 pairs of appendages. 



Zoea, more than eight but not more than thirteen pairs 

 of appendages. 

 An obvious objection to the scheme is that Euphausia, for 

 example, i? bound to pass through a zoea stage to reach a megalopa 

 condition. But I have chosen to define the stages with reference 

 to a state of full development, for the reason that if we take into 

 consideration the appearance of all the appendages we should 

 want to define not four stages but some sixteen. I hope at least 

 in drawing attention to the problem I have paved the way to a 

 solution, and that writers on the subject will cease from calling 

 by the same name such obviously different stages as the newly 

 hatched larvae of the crab and the lobster. 



2._GR0WTH. 



The preceding section will serve to explain the modification 

 of the nomenclature which is employed here to distinguish the 

 larvae. The larvae, as has been seen, are hatched with a certain 

 number of appendages, and a series of ecdyses allov^^ of the develop- 

 ment and the growth of the remaining limbs. This is accom- 

 panied by an increase in size. After the larval stages have been 

 completed, the subsequent advances in growth are brought about 

 by further ecdyses. These as a whole gradually become separated 

 by longer intervals of time, but the intervals are also subject to 

 some degree of variation by season, the ecdyses tending to be 

 more numerous in the warmer months. A sudden increase in 

 growth takes place usually at each ecdysis, but a continuation 

 of growth may take place during a short period after the ecdysis 

 has occurred. It might therefore be more accurate to express 

 the increase in graphs such as those which have been made to 

 illustrate this section by steep curves, but as the growth which 

 succeeds the ecdysis is small compared with that which is the 

 result of the process and the time with reference to the instar is 

 short the growth is expressed as accomplished at the ecdysis. 



Brachyura. — The growth of the shore crab, Carcinus maenas, 

 can be stated with an approach to accuracy for G. Brook and Mr. 



