REPORT OF COMMISSIONERS OP INLAND FISHERIES. 55 



but such instances are not numerous, so that the change may be 

 called most characteristic of the sixth stage lobster. (Plate XII.) 

 The same facts hold true in regards the appearance and develop- 

 ment of the external reproductive organs. Very often these may 

 be observed in the sixth stage as small buds upon the under side of 

 the first abdominal segment. They may not, however, appear until 

 the seventh stage, and even then they are seldom developed beyond 

 the bud stage. The differentiation of the sex of the young lobsters 

 can not be made clear by this means until the eighth or sometimes 

 the ninth stage. The sex, however, can be determined earlier by 

 observations of the openings of the egg or sperm duct upon the basal 

 joint of the first and third ambulatory appendages, respectively. 



Seventh to the Twelfth Stages. 



The changes in form, if any, which may occur in the course of de- 

 velopment from the seventh to the twelfth stage are too slight to be 

 determined by any method yet devised. It is entirely possible, 

 however, that continued observations may reveal some point which 

 may be taken as a constant stage-criterion for these later stages. 

 And yet, on the other hand, it is c{uite probable that, so far as the 

 greater number of discriminating facts is concerned, the rapidity of 

 assuming structural conditions which might be characteristic of a 

 certain stage is much dependent upon the strength or vitality of the 

 individual lobster and upon the conditions of its euA-ironment. The 

 young lobster, with few exceptions, assumes the adult color type 

 when it enters the eleventh stage of its existence. The question now 

 arises whether or not there is a definite stage in which the young 

 lobster assumes its adult structural form; or is there a definite stage 

 wherein it arrives at an adult functional condition. It is quite 

 probable that further observations may demonstrate the truth of 

 the former hypothesis,* while in regards to the latter, the develop- 



* Observations at the present date would indicate that the adult structural type is reached 

 in the ninth stage. 



