322 BULLETIN OF THE BUREAU OF FISHERIES. 



When a bottom life is finally adopted, the instincts of burrowing, hiding, wariness, 

 pugnacity, and preying become strongly accentuated. The animal is negatively photo- 

 tactic and tends, as in all later stages upon the whole, to avoid strong light. 



In the larval lobsters the big claws are prehensile organs solel}'; by which the food 

 is seized and transferred to the mouth parts. At the fourth stage the great double 

 claws are perfectly developed, similar in structure, and of the primitive toothed type. 

 The smaller chelse and other appendages are in perfect symmetry. At about the sixth 

 or seventh stage a difference in the big claws begins to appear, the claw on one side 

 developing crushing tubules and becoming larger and heavier in accordance with the 

 greater development of its muscles. The smaller forceps, the jaws of which have 

 developed serially arranged teeth, retains its primitive form. Whether right or left 

 claw shall be of the toothed or crushing type is predetermined in the egg, all members 

 of the same brood in all likelihood being either right-handed or left-handed. (See p. 274.) 

 Injury or mutilations, however, may determine the position and character of the claw 

 in after life. 



At the seventh molt the cast shell is blue with some green and brown pigments 

 on the tergal surfaces. Pigment is thenceforth more and more deposited in the outer 

 calcified layer of the shell, which becomes wholly responsible for the color of the animal. 

 The dorsal median stripe of the carapace, which marks an absorption area of distinct 

 service in molting, is much narrower than when first observed in the fourth stage. At 

 the time of the fourth molt this linear area is one-eighteenth of the width of the carapace 

 at its widest part. It gradually narrows until in the adult state it is in the proportion 

 of one-sixtieth or less. 



The sex can be determined as early as the eighth stage by the openings of the sexual 

 ducts, which in the male arise in the coxa or basal segment of the last pair of thoracic 

 legs and in the female on the coxae of the third pairs of pereiopods. The sex can not 

 be determined by the modified swimmerets of the first abdominal somite until some time 

 between the eighth and the tenth molt. At about the eighth stage also the peculiar 

 seminal receptacle of the female begins to undergo its characteristic differentiation. 



During the adolescent stages, when the lobster of either sex measures from i^ to4 

 inches in length, there are certain marked characteristics— the relatively large size of 

 the eyes, recalling those of the shrimp PencBus setiferus and probably a relic of an 

 ancestral stage, the fringe of long setae on the tail-fan, and the tufts of hairs about the 

 ends and along the serrate jaws of the toothed claw. 



With this introductory sketch, we will examine more closely the embryo and larva, 

 although it is not our intention to enter minutely into all the details of their structure. 



EMBRYO. 



The freshly laid eggs are dark green, almost black in color owing to the presence 

 of the soluble pigment, a lipochromogen, in the yolk, and the glass-like transparency of 

 their membranes. (Compare p. 298.) The golden yellow variation, which is often 

 associated with dark green, as in the eggs of certain shrimps, has not been observed in 



