76 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



7. The average length of the fourth stage lobster is about 13 

 mm. ; it is now almost the epitome of the adult lobster. 



In the succeeding stages of the j^oung lobster many of the changes 

 which take place may be noted, not so much with reference to any 

 definite stage as with regards to the continued development as a 

 whole. Of these we may note the following: 



1. The eyes become less and less prominent as the stages advance. 



2. A broadening and thickening in the body occurs. 



a. In the male this takes place in the cephalo-thorax. 

 6. In the female, the broadening is in the abdomen. 



3. There is a thickening and strengthening of all the body ap- 

 pendages with a gradual variance in the appearance of the right and 

 left chelse. 



Fifth Stage. 



The fifth stage lobster is too immature to at once manifest many of 

 these changes; the chief characteristic of this stage being the promi- 

 nence of the basal joints of the first antennae, as in contrast to this 

 position under the rostrum border in the fourth stage. (Plate XI.) 

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



Sixth Stage. 



The point of distinction of the sixth stage is the beginning of a dif- 

 ferentiation in the shape of the chelse, the right manifesting a tendency 

 to develop into the "nipping" claw, the left into the "crusher." 

 This change sometimes is not evident until the seventh stage. The 

 external reproductive organs often make their appearance in this 

 stage. They first appear on the under side of the first abdominal 

 segment. This phenomenon may, in some cases, be delayed until 

 the seventh stage. The sex, however, can often be made out in the 

 sixth stage by the position of the openings of the sperm ducts or 



