268 



BULI/ETIN OF THE BUREAU OF FISHERIES. 



3?IG. 1 7. — Outline of great claw tip, showing serrate margin of proj 

 podus. in first larval stage of the lobster, represented as a trans- 

 parent object, from glycerine preparation. Note the invagi 

 nated sensory hairs or setae (s), and claw-tip it s), and three 

 teeth of the first order (i, I, i) developing from apex to base^ 

 and representing the three primary periods (i, n, m), indicated 

 in figtu-es 11 and 18; also a tegumental gland opening at the 

 tip of each of the two oldest spines. 



When these claws are magnified thirty or forty times (fig. 15 and 16) the first steps 

 in the differentiation of the crushing from the primitive toothed type of claw become 

 evident. They are expressed by a blunting or rounding off of the sharp points of the 

 teeth, and a tendency to fusion among those situated at the proximal extremity of both 

 divisions of the claw. (Compare fig. 21-24.) 



We therefore conclude that during the fourth, fifth, and in some cases at least in 



the sixth or even seventh stages of the 

 lobster, both of the big claws represent 

 the older or phylogenetic type which is 

 retained as the toothed or lock forceps of 

 the adult. The chela destined to become 

 the crusher is a little broader • though 

 not necessarily longer than its fellow, and 

 its teeth which still show the periodic 

 sequence are more rounded, as we have 

 just seen, at the proximal end of the series. 

 The tufts of sensory hairs are, moreover, 

 less prominent on the future crushing 

 claw, as apparent in all the later'stages. 



The development of the toothed type 

 of claw is represented by a series of draw- 

 ings (fig. 17-25, andpl.xi,ii)from thefirstto the ninth or tenth stages, in which theorderly 

 appearance of the spines can be followed with approximate accuracy up to stage 3, and 

 with certainty beyond it. The large propodus only is represented in most of the figures. 

 The spines of the toothed claws are developed in a linear series, and the order in 

 respect to size corresponds to that of age, or time of appearance. The larger teeth of 

 the first order are the first to 



emerge. They are set at wide in- \^ , - jJ 



tervals and evenly spaced. From 



2 to 3 are recognized in the chelae 

 of the first larva (fig. 17) and from 



3 to 5 in the claw of the second 

 stage (fig. 18). In the third stage 

 the normal number of primary 

 teeth are present (fig. 19), although 

 some of them are very small, and 

 in the intervals between them are 

 interpolated rudiments of the teeth 

 of the second order. In a single series the first trace of the third series of teeth may 

 be detected also. At the fourth molt (fig. 20) a single period of eight may be com- 

 pleted by the intercalation of the four small teeth of the fourth order ; but the process does 

 not always stop here, and an attempt, so to speak, is often made at the seventh, eighth, 

 or at some subsequent molt to introduce a fifth series of 8 teeth, which if completely 



Fig. 18. — Outline of corresponding part of big claw shown in figure 17, but in 

 second larval stage, showing the separated primary teeth, invaginated 

 claw-tip, and setse, as well as a new spine arising at either end of the 

 series. Spine i of period m now bears the duct of a gland. See figure 11. 



