334 BULLETIN OF THE BUREAU OF FISHERIES. 



The exopodites atrophy, and are reduced to microscopic rudiments in the fourth 

 stage, and completely disappear in the fifth. No doubt in this respect there is variation, 

 however, as Williamson {282) has found to be the case in the European lobster. 



In rising with head inclined, the body is usually bent into a quadrant, and according 

 to Hadley {131) when the appendages are extended forward the exopodites strike 

 somewhat forward as well as downward and thus drive the lobster upward and backward 

 (fig. 40, c) ; when on the contrary the thoracic legs are contracted or drawn backward 

 the larva is driven forward and upward. Whatever the direction of movement, as this 

 observer has also pointed out, the animal always heads away from the source of light. 

 In swimming near the surface the thorax is sometimes held horizontal with tail bent at 

 an angle of 45°, more or less (o) ; when riding down another larva, feeding upon its carcass, 

 or grappling with a lobster's egg the body is straightened (6) ; in the ascending currents 

 of a hatching jar the young frequently come to the surface tail uppermost, and body 

 vertical (d). By bending the body the weight is concentrated, which is especially advan- 

 tageous in swimming upward. As Williamson remarks, the position of the body is 

 correlated with the beats and direction of motion of the exopodites. 



In hovering over the bottom, "standing on their heads," and as it might appear, 

 probing the sediment with the rostrum (fig. 40 /), they are not trying to escape the light, 

 as one observer has suggested, but are oriented for rising, being too weak, however, for 

 any sustained effort. In every hatching jar or container many weakened individuals 

 gradually settle into the sediment, a veritable trap for them, at the bottom, at first 

 kicking away with strokes of the tail or standing erect with every oar in motion, but 

 finally keeling over on their backs and beginning the death struggle to which there is 

 usually but one ending. 



The mutual destructiveness of the young lobsters when too closely crowded in 

 aquaria has already been mentioned. When one lobster attacks another under these 

 conditions the pursuer usually endeavors to get astride of his victim and with its sharp- 

 pointed prehensile legs nip into the abdomen at its junction with the carapace. When 

 the prey is an object too heavy to float, the lobster is frequently carried to the bottom; 

 but if the animal is healthy it will be usually seen swimming about the aquarium drag- 

 ging its prey with it and feeding upon it as it goes (fig. 40 h). 



The beating of the heart and circulation of the blood begins at about the fifth 

 week of egg development, or even earlier, and in the larval stages the heart and blood 

 vessels have acquired the same general relations that we find in the adult. 



The lobster at first possesses 19 pairs of filamentous gills distributed as in adult 

 lobsters. The podobranchs are rudimentary, as are also the gill separators or epipodites, 

 which are minute reniform plates exposed below the free border of the carapace. In 

 the second stage these plates are taken completely into the gUl chamber and the 

 rudimentary gill of the eighth somite appears, which completes the branchial formula 

 (see p. 246). 



The nervous system of the lobster is highly developed in the larva and indeed 

 before hatching, as shown by the admirable researches of Allen, (2), and brain, nerve 



