54 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



of the eggs which are borne under the "taih" There is also evident 

 a gradual thickening and strengthening of all the body appendages, 

 which, in the fourth stage are relatively rather light and frail. 



Fifth Stage. 



The fifth stage lobster is still too young to manifest these changes in 

 any appreciable degree, either in form changes or in sexual differences. 

 It is very often possible, however, to distinguish the fifth from the 

 fourth stage lobster, although the differentiation depends upon very 

 minor characteristics. In the fourth stage the basal segments of 

 the first pair of antennae are, when viewed in the dorsal aspect, well 

 concealed beneath the margin of the projecting rostrum. In the 

 fifth stage there is usually a greater prominence in the position of 

 these basal antennal segments, so that they may be seen in dorsal 

 aspect projecting from beneath the anterior portion of the rostrum 

 border. (Plate XL) The peak of the rostrum itself, moreover, 

 undergoes a slight series of changes which occur fairly constantly in 

 the development through the fourth, fifth, and sixth stages. These 

 changes may be best noted by a glance at the diagrams in plate XX. 

 The average length of the fifth stage lobster is 15-16 mm. 



Sixth Stage. 



By any differences in general morphology it is difficult to tell the 

 sixth stage lobster from the fifth, since the general body form and 

 appearance of the appendages is very similar in both stages. The 

 chief point of difference lies in the fact that, whereas in the fifth stage 

 lobster the left and right claws or chelae were exactly similar in ap- 

 pearance, in the sixth stage there is in a large number of cases the 

 beginning of a differentiation into the characteristic "nipping" and 

 "crushing" claw, the former normally upon the right, the latter on 

 the left. (Plate XIX.) This change comes about through a widen- 

 ing of the "crushing" claw, while the right, or "nipping," claw re- 

 tains a close resemblance to that of the preceding stage. In some 

 cases this claw differentiation does not occur until the seventh stage. 



