67 



by marking experiments. Marking experiments have demon- 

 strated also that as the females become mature they migrate 

 from the Northumberland coast to the region of the Firth of Forth, 

 some still further to the north, and they may attain to the Moray 

 Firth. It is after migration that the females come into berry, 

 as the act of spawning is termed. After the ova are hatched, 

 ecdysis takes place, and with ecdysis, pairing. It is evident there- 

 fore that the crabs at this stage are once more in the condition of 

 those marked originally on the Northumberland coast, and that 

 therefore when they become mature, that is when the gonad once 

 more commences to develop, the migration will be still again in 

 a contranatant direction. The interesting feature of difference 

 in the crab as compared with the fish is that the female only 

 migrates for spawning. As has been said, pairing takes place 

 during the ecdysis of the female, and the gonad of the female 

 may not commence to develop until long after the event. It is 

 then that the hormone is produced. The ripening of the male 

 gonad is not accompanied by migration, and it would be interest- 

 ing to know whether this is due to the hormone being withheld 

 or its effects inhibited. 



We are led to conclude therefore that the spawning migration 

 is due to the action of an internal secretion, and is a special mani- 

 festation pioduced by the same or a similar cause as that which 

 makes a buck mad in November and a hare in March. In many 

 cases somatogenetic results are produced, but the effect we have 

 to note in fishes is the contranatnat migration which brings about 

 congregation. We have seen reason to conclude also that the 

 stimulation is not the same with reference to the sexes, and indeed 

 may be very different, but with fishes as a rule it is complimentary. 

 It has been observed in several cases of assembling for spawning 

 that the males arrive first and occupy the region during the 

 spawning season, while the females enter the region when about 

 to spawn, and leave after the operation is ended. The spawning 

 event, however, of the female is not continuous, but is spread over 

 one or two weeks, a succession of spawnings being separated by 

 several days of rest.* 



Spawning therefore is concentrated in particular regions 

 which have been specified and more or less well demarcated from 



* Report, 1011, p. 24. 



