304 BUI,I.ETIN OF THE BUREAU OF FISHERIES. 



The brush-picks of the lobster, especially those on the last two pairs of ambulatory 

 legs, resemble similar instruments in the crayfish, as described by Andrews, and there 

 can be no doubt that they serve a like purpose. That they are used as cleaning brushes 

 has been often observed, but no one has yet studied the behavior of the lobster in the 

 critical period before egg laying is accomplished. 



Nevertheless I have recorded an observation {149, p. 47) which, read in the light 

 of the foregoing account, suggests that the lobster has the cleaning instinct also and 

 carefully prepares her abdomen for the reception of the ova. In two cases which I 

 had been watching the lobsters laid their eggs in aquaria, and then industriously picked 

 and scratched off nearly every one of them in the course of a few days. Now, these eggs 

 were all of small size and the ovaries did not give up more than a third or a half of 

 their contents. Under these conditions it would not be surprising to find the attunement 

 of the instincts at fault. Interpreted in this way, the lobster by cleaning off her eggs 

 was only preparing herself for the reception of the ova which still clogged the ovary. 



In the lobster the terminal joint or dactyl of the last pair of legs {cl. br., fig. 4, pi. 

 xxxviii) is developed as brush and pick, there being no comb on the under side. It is 

 cone-shaped and traversed from apex to base by three nearly equidistant rows of hairs 

 or setse, those of the upper row being long, dense, and serrated. The subterminal joint 

 bears three conspicuous tufts of saw-tooth hairs, quite similar to the "scouring brushes" 

 described for the crayfish. In place of the strong spines or picks on this segment of the 

 Cambarus is a single blunt spur almost concealed by the brush of hairs in the lobster. 

 Just above it, near the base of the line of long dense setse is a rudimentary comb or 

 short linear series of spines. 



If the short process which bears two spurs or picks in Cambarus were extended, it 

 would form, as Andrews suggests, a double claw or forceps similar to those of the smaller 

 chelate legs. In this case, however, the chete would all have the same relative posi- 

 tions or work in parallel planes. In the second and third cheUpeds the claws work 

 up and down, or in a nearly vertical plane, on the hinge joints. The great claws, how- 

 ever, have undergone a twist or torsion, in consequence of which their inner or anterior 

 surfaces have become their lower sides. (See p. 257.) The dactyls consequently face 

 and open inward, working in a horizontal plane. Now, the terminal segments of the 

 last pair of legs have suffered a backward rotation or twist, in consequence of which their 

 anterior surfaces are directed obliquely outward. If this limb were chelate, the dactyl 

 would move obliquely outward and backward instead of upward, as in the smaller 

 chelipeds, or inward, as in the great forceps. 



In the lobster the torsion of the two terminal segments of the fifth pair of walking 

 legs has gone a step further, so that the comb and spur of the dactyl, instead of being 

 on the lower and anterior side of the limb, as in Cambarus, axe. upper and hindermost 

 in Homarus, and, further, they no longer lie midway between the hinges of the joint, as 

 in the crayfish. The torsion and other adjustments in the fifth pair of legs in the lobster 

 evidently fit them for reaching and brushing the swimmerets and under side of the tail. 



