352 BULLETIN OP THE BUREAU OF FISHERIES. 



At certain points on the coast it may be possible to rear many marine animals 

 with comparatively little difficulty, or to keep them alive in the adult state for long 

 periods, while at other places every aquarium may become the grave of all but the 

 hardiest species or individuals, and that in a short time. The difficulty seems to arise 

 from the nature of the plankton, and from the tendency of certain prevalent organisms, 

 such as diatoms, parasitic bacteria and fungi, to increase in an inordinate degree. The 

 larvae become weakened, and can not pass their molts. 



(7) In the fourth stage the young lobster, as if in one bound, seems to justify its 

 name, to lose its old swimming organs and acquire new ones, to lose the rolling uncer- 

 tain gait of the larva and to acquire new strength with greater precision and speed. It 

 loses in large measure its former transparency, and, together with a greater hardness 

 and opacity of its shell, it gains a far greater brilliancy and variety of coloring. The 

 fourth stage also marks the rise of new instincts such as fear, burrowing for concealment, 

 not to speak of far greater pugnacity, and the dawn of intelligence or power of associa- 

 tion, displayed in the lobsterling's holding to the same hole or retreat for hiding, to 

 which it will return repeatedly and will defend with spirit. Perhaps more important 

 than any of these characteristics is the fact that many of the fourth-stage lobsters 

 probably go to the bottom and stay there. This at least is their habit when reared in 

 confinement. 



The fourth-stage lobsters seem to swim at the surface more regularly and con- 

 tinuously than the larvae, and accordingly are more often taken in the net, while it is 

 evident that the earlier stages must be thousands of times more numerous. 



(8) The rate of growth is greatest during early life, and according to Hadley is 18 

 per cent at each molt at Wickford, R. I., up to the seventeenth stage, when it begins 

 to slowly decrease. I found the rate to be less in the slightly colder waters at Woods 

 Hole in the case of artificially hatched and reared young. The time interval be- 

 tween successive molts is indeterminate, being subject to every change which affects 

 the physiological vigor of the animal. The advancement of the larva is to be measured 

 by the number of its molts and not by its age. Under favorable conditions the three 

 larval stages are passed in 10 or 12 days; the fourth stage lasts as long, so the swim- 

 ming period may be over in about three weeks, or may be extended to four weeks or longer 

 when the bottom is not sought until the fifth stage. 



The approach of the molt seems to start the lobsterling on its course to the bottom ; 

 accordingly when this is delayed until after the fourth stage, it probably does not often 

 occur until the approach of the succeeding molt. (See p. 348.) 



