340 BUI.I.ETIN OF THE BUREAU OF FISHERIES. 



onward there is a gradual forward movement of the appendages — maxillae, maxillipeds, 

 and pereiopods — until the fourth stage, when they attain essentially their adult condi- 

 dition. Average length of third larva, Woods Hole, Mass., ii.i mm.; extremes, io-12 

 mm. (79 measurements); Wickford, R. I. (Hadley f or 1904), average length, 11.4 mm.; 

 stage period, 5 days. 



THE FOURTH OR LOBSTERLING STAGE. 

 [Plate XXXI.] 



The young lobster makes a surprising leap at the fourth molt, or the third after 

 hatching, when suddenly it seems to undergo a literal metamorphosis and to become a 

 new animal, and when for the first time it truly resembles a diminutive lobster. In form, 

 color, habits, and instincts it differs strikingly from every preceding stage. 



The oars or swimming exopodites of its twelve thoracic legs are reduced to func- 

 tionless stumps, which as a rule are no longer visible to the naked eye. Yet it still 

 swims at the surface with greater agility, precision, and speed than at any former stage. 

 The balancing organs, formerly called the "otolith sacs," at the base of the first pair of 

 antennae, are fully developed, and the reeling, uncertain gait of earlier stages is no longer 

 observed. Nor is the body bent in swimming, but is straight as an arrow, and as the 

 lobsterling glides swiftly along by the action of its swimmerets, now for the first time in 

 complete working order, the big claws are extended straight in front of the head and 

 held close together. WhUe it uses the same organs in swimming as an adult animal, 

 unlike an adult it swims at the surface and with a relatively much higher rate of speed. 

 As in earlier stages it darts backward by quick jerks of the abdomen, according to one 

 observer even jumping out of the water, a feat which it is never again able to perform, 

 and which is possibly equaled in the higher Crustacea only by certain kinds of surface- 

 feeding shrimp. The great chelipeds are long, slender, and end in symmetrical claws 

 of the toothed type. 



The incessant and apparently aimless activity of the young in all their swimming 

 stages has been often remarked. While this activity does not protect them from their 

 enemies or enable them to stem a current of much strength, it is not useless, for it en- 

 ables them to keep afloat and thus brings them into contact with suspended food, which 

 has been found to be an important requisite in every hatchery. It has been further 

 observed that when at apparent rest the motion of the swimmerets in the third and 

 fourth stages tends to keep the little lobster from sinking. 



Like the larvae, the fourth-stage lobsters continue to feed on copepods and small 

 pelagic organisms of various kinds, even snapping up floating insects, according to Wil- 

 liams (279), who saw a swarm of lobsterlings seize, drag under, and devour a full-grown 

 cricket which happened to fall into their tub. 



In a number of fasting fourth-stage lobsters, which Williams also examined, the 

 stomachs were found to be empty or to contain only masses of clam cuticle, which they 

 commonly reject, from which it appeared that such lobsters, even when very closely 

 confined in a finger bowl and "hungry enough to eat what they ordinarily refuse, will 

 not attack one another (unless perhaps one or more of their number is newly molted)." 



