138 Proceedings of the Royal Irish Academy. 



become so fiequeiit Lliat, assuming that the growth periods represent years, 

 it is not possible to assign a definite age to any particular fish. Tlieoretically, 

 if this were the full explanation, the scales showing the minimum number of 

 rings ought to give the maximum age which can be assigned to the fisli ; but 

 thei'e appears to be a further complication in that all tlie normal growth 

 periods are not represented on every scale. This is evident from the faettliat 

 uuregenerated scales may be found showing no signs of growtli-rings. 

 Although the conditions of temperature and light and, probably, food supply 

 are, even at about 500 fathoms, not subject to any significant annual 

 variations, it is not incredible that annual periods of growth should exist 

 witliout an external stimulus, owing to some inherited habit either of migration 

 from greater to lesser depths, or of feeding, or even to some inherited 

 physiological rhythm. 



