58 THE ROYAL SOCIETY OF CANADA 



and is able to move only at a very slow rate, there is no opportunity 

 for the young to have an essentially different distribution from that of 

 the adults. It does not appear to be found in the deep ice-cold water, 

 being replaced there by other species of the same genus. The star 

 fish resembles the sea-urchin in having the young distributed in very 

 shallow water, but we were unable to determine the distribution of 

 the adults on the Cheticamp slope. At the Magdalen islands the 

 young were found in shallow water and the adults only at greater 

 depths, namely, from fifteen to thirty metres, at which depths inter- 

 mediate conditions of temperature prevail. On the Cheticamp slope 

 similar conditions are not to be found at any level, except temporarily, 

 because of the extensive vertical oscillations of the warm and cold 

 water, which are efl'ected by the action of the wind on the warm sur- 

 face water, driving it to or from the coast. Were it not for the com- 

 paratively steep nature of the slope of the bottom off Cheticamp, 

 this would not be possible. We can explain our failure to find large 

 starfish {Asterias vulgaris) on the Cheticamp slope, only by the sup- 

 position that they are killed off in early life by the alternation of very 

 warm and very cold conditions, that slope affording them no place 

 where the intermediate conditions necessary for their existence are 

 to be found permanently. Seeing that their early stages are pelagic, 

 their larvae borne from spawning grounds elsewhere in the gulf will 

 yearly settle in the shallow water along shore, but there will be no 

 possibility of the species obtaining a permanent foothold in the 

 region. In the deeper ice-cold water it does not occur, but its place 

 is taken by an arctic species, — Asterias polaris. 



The distribution of these species is shown in figure 2 beside the 

 column representing the conditions in the water. 



The conditions of temperature and salinity in the water at the 

 two localities, which are to a considerable extent correlated with 

 the amounts of the tidal amplitude, are given in the figures (1 and 2) 

 from determinations made by Professor A. Vachon for the latter part 

 of the summer, at the time the distribution of the species of animals 

 was investigated. The depth of the superficial stratum of warm 

 water at Cheticamp exhibits great variations within short periods of 

 time, these variations depending principally upon the direction and 

 strength of the wind in the adjacent portion of the gulf. We have 

 represented the depth of this layer in what is probably its maximum 

 condition* 



It may be considered as practically certain that the depth of this 

 superficial stratum of water with a comparatively high temperature 

 and low salinity, which at the same time involves a very low density, 

 is the factor which determines the upper limit of distribution of such 



