532 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



particular individual remained in this stage was observed only a few 

 times. One full-grown zoea (like the specimen figured) obtained June 

 23, and placed in a vessel by itself, changed to a megalops between 9 

 and 11^ a. m. of June 24, and did not molt again till the forenoon of 

 June 27, when it became a young crab of the form described farther on. 

 Of two other zoese obtained at the same time, and placed together in a 

 dish, one changed to a megalops between 9 and 11£ a. m. of June 24, 

 the other during the following night ; these both changed to crabs dur 

 ing the night of June 26 and 27. 



The following memorandum on a large number of the same lot of both 

 stages of the young, kept together in a vessel of fresh sea-water, also 

 indicates the rapidity of these changes. In the columns "zoea" and 

 " megalops" the total number of individuals in each of these stages is 

 given; under "crabs" the number which had appeared since the last- 

 observation, and under "dead" the number which had died since the 

 last observation : 



Time of observation. 



Zoea. 



Megalops. 



Crabs. 



Dead. 



June 23, 7 p. m 



15 

 5 

 4 

 2 

 1 

 



22 



23 



22 



22 



22 



20 



19 



16 



14 



12 



11 



9 



4 



2 





 2 

 2 

 1 

 1 

 

 1 

 1 



2 

 

 

 2 

 3 

 2 







June 24, 5 a. m 











June 24, 114 a. in 



1 



June 24, 7 p. m 







June 25, 6 a. m 



3 













2 











June 27, 24 p. ni 





9 



June 27, 7 p. m 





1 



June 28, 7 a. m 









June 28, 4 p. ni 



■ 



2 



June 29, 7 a. m 













In the two or three instances in which the change from the megalops 

 to the young crab was actually observed, the megalops sank to the bot- 

 tom of the dish and remained quiet for some time before the molting 

 took place. The muscular movements seemed to be much less violent 

 than in the molting at the close of the zoea stage, and the little crab 

 worked himself out of the megalops skin quite slowly. For a short time 

 after their appearance the young crabs were soft and inactive, but the 

 integument very soon stiffened, and in the course of two or three hours 

 they acquired all the pugnacity of the adult. They swam about with 

 ease and were constantly attacking each other and their companions in 

 the earlier stages. Many of the deaths recorded in the above memo- 

 randum were due to them, and on this account they were removed from 

 the vessel at each observation. In this early stage the young crabs are 



