Hadley, Behavior of the American Lobster. 259 



thorax, which in turn is indined about 30° from the hori- 

 zontal plane. In daylight this position may be maintained with- 

 out modification for several minutes, but the equilibrium is often 

 interrupted by other body-movements w^hich, upon superficial 

 examination, appear to be of a most diverse and ill-ordered nature. 

 There are leanings, turnings, fallings, somersaults, revolutions 

 and rotations which follow each other in no apparently definite 

 sequence, and which disturb the general equilibrium greatly or 

 slightly as the case may be. 



Whether the balanced equilibrium, the devious rotations or 

 other activities are present, the exopodites or swimming attach- 

 ments of the thoracic appendages beat the water more or less con- 

 stantly with short vibratory strokes, sometimes lifting the larvae 

 high toward the surface, and again allowing them to sink to the 

 bottom, where they frequently lie for some moments almost motion- 

 less, only again to resume their varied activity. Now they swim 

 forward, now backward, now lurch to the side, now to the rear, 

 always maintaining more or less energetically these apparently 

 aimless movements. Such is the nature of the swimming in day- 

 light or other brilliant illumination; but for our purpose it cannot 

 be called the normal swimming of the lobster larvae. It is only 

 under special conditions that the latter may be observed; and, in 

 view of the fact that it is the conditions of light which influence 

 more strongly than any other factors the behavior of the larvae, 

 it is only when they are under certain light-conditions that we 

 may expect to find manifested what we may call the characteristic 

 or normal swimming. 



The twilight or nocturnal swimming of the larval lobsters inva- 

 riably gives us the fairest example of natural behavior. At such 

 times alone (or when the larvae are submitted to artificially pro- 

 duced twilight) variations in temperature and the multiplicity of 

 conflicting cross-light influences are eliminated. Frequently when 

 the twilight was so dim that observation was rendered difficult, 

 the swimming was delicate and regular, and the young larvae would 

 mount up, bird-like, to the surface of the water, hover many sec- 

 onds in a single position, or swim backward or forward with equal 

 ease. In such a case, when a lighted match was brought near the 

 side of the jar in which the larvae were confined, the same restless and 

 uncertain swimming, characteristic of the diurnal activities, was 

 again manifested, together with the accompanying leanings and 



