172 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



HABITS. 



The habits of young lobsters differ but little during the various "stages" of their 

 free-swiinming life, which is spent near the surface. Their pugnacious instiuct is 

 undoubtedly strongest immediately after hatching, when their activity in killing and 

 devouring one another invariably attracts the notice of the spectator and forms an 

 insurmountable barrier to raising them in small aquaria. Like the young of most 

 pelagic organisms, they can not bear crowding, either in vertical or horizontal limits. 

 As Weldon and Fowler (201) have remarked: 



They must, if they are to thrive, have a large superficial range, as well as a considerable depth 

 of water in which they may sink when such conditions as light and heat demand it. 



In swimming the larva? use both the exopodites of the thoracic limbs, by the beating 

 movements of which they are impelled upward and forward, and the abdomen, by 

 the contraction of which, with its broad telson-plate, they dart rapidly backward. 

 Each thoracic limb consists of a short stalk, with two diverging branches, the outer 

 branch, which serves as an oar, being flattened and fringed with long feathered hairs. 

 The oars or exopodites work independently of the inner branches, which are mainly 

 prehensile organs, and alone give rise to the adult limb. The exopodites atrophy and 

 disappear completely after the fifth stage. In the common swimming or floating 

 position at the surface the thorax is usually held in a horizontal position, with bent 

 abdomen. In rising the head is inclined downward, often with the "tail" uppermost. 

 When too weak to keep at the surface, they vacillate over the bottom, standing on their 

 head, as if probing for food, which, however, is not the case. 



The larvae appear to be quite hardy under certain conditions. Thus I have kept 

 them alive, and apparently healthy, in small flat dishes of sea water, without change, 

 for from one to four days at a time, or until they molted to the second stage. 



The time which elapses between two successive molts varies, as at all subsequent 

 stages, with the supply of food and general condition of the animal. lu the larvae 

 which I had under observation the first stage lasts from one to four or five days, the 

 healthier ones molting in the shorter period. 



THE SECOND STAGE. 



All the larvae of this stage which I have examined were raised from the egg. 

 The average length in forty-seven cases was 9.2mm., the extremes being 8.3 to 10.2mm. 

 It is evident that some of these were undersized, and the measurement of this stage 

 given by Professor Smith, 10.6, is greater than any which I have observed. His speci- 

 mens were all taken by the towing net, and if the number examined was sufficiently 

 large it would indicate that under natural conditions a greater size is attained. 



A profile view of the second larva is given in plate 21. This is drawn to the same 

 scale as the first larva on plate 20, and illustrates the increase in size effected at 

 the second molt. All parts are now much larger, excepting the swimming thoracic 

 appendages, which have grown but little. The swimmerets, visible as buds below the 

 cuticle of the first larva, have now grown out on the second to fifth abdominal somites, 

 and the rudiments of the last pair of appendages can be seen beneath the skin at the 

 proximal end of the telson plate (fig. 102, plate 34). 



The habits of the second larva differ in no respect from those of the first, and in 

 color the two stages are very similar. In transparent larva', with contracted chroma- 



