46 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



are concerned with the reproductive organs as the young lobster 

 approximates to the adult structural and adult functional type. Of 

 this last problem, however, concerning the internal changes, it is not 

 the purpose of this paper to treat, its scope being limited to a con- 

 sideration of the changes in the external structure. This may 

 properly include the general body form and the changes which take 

 place in the swimming, ambulatory, or sensatory appendages, show- 

 ing how they differ from one stage to another. 



I. The Changes of Form in the Successive Stages of the 



Lobster. 



The First Larval Stage. 



When the egg membrane has burst and the j^oung lobster is libera- 

 ted, it presents an appearance little resembling the adult. Owing 

 to the coiling of the abdomen and infolding of the appendages while 

 still within the egg, the young lobster emerges with the abdominal 

 portion curved anteriorly around the head, the final segment lying 

 over the rostrum or beak. This is also folded downward and in- 

 ward, the whole form of the animal thus approaching oval shape. 

 It is but a few moments after the young lobster is freed from its 

 egg-membrane that several changes occur. The abdomen gradually 

 bends away from cephalo-thorax, the tail fan broadens, the antennse 

 project forward, the exopodites of the thoracic appendages (which 

 heretofore have lain folded over and somewhat between the legs) 

 straighten and become functional, beating the water with short 

 vibratory strokes, and the first stage lobster, now about 8 mm. in 

 length, begins to shift for himself. 



During the progress of the first stage the body form undergoes but 

 slight change. There is noticed only the gradual extension of the 

 abdomen and rostrum which, to the end of the stage, forms a de- 

 cided arc with the dorsal surface of the cephalo-thorax. There is 

 also a somewhat greater projection of the eyes and a widening of 

 the ventral and lateral region of the cephalo-thorax, due probably 



