1 78 . BULLETIN OF THE BUREAU OF FISHERIES. 



attained by our more inclosed waters during the hottest part of the summer. For the 

 great majority of cases, it must be admitted that this explanation is wholly conjectural. 

 We know of at least one species of animal, however, which occurs in an active condition 

 throughout Vineyard Sound during the winter and spring, but which, in these waters, 

 passes into a condition of aestivation during the summer. This is the hydroid Tubularia 

 couihouyi (see p. 565). Now it is of significance that in the colder waters at Crab Ledge, 

 and beyond Marthas Vineyard, at a depth of 29 fathoms, active hydranths of this species 

 have been dredged by us in July and August. Certain others among our local hydroids 

 are likewise known to be dormant, or at least less active during the summer months. It 

 is quite conceivable that at somewhat higher temperatures such species would be 

 destroyed altogether. 



We may say, then, that while there is some evidence for the operation of the principle 

 of Merriam, in both of its phases, in determining the distribution of marine organisms 

 in local waters, it seems likely that no single formula will suffice to explain all the phe- 

 nomena involved; " and it is certain that we can form no adequate explanation of these 

 until vastly more data are at hand. Both observation and experiment are demanded. 



4. THE INFLUENCE OF DEPTH. 



The great majority of species which were dredged by us in Vineyard Sound and 

 Buzzards Bay were found to have a distribution, in local waters, which plainly bore no 

 relation to depth. There are notable exceptions to this statement, however, some of 

 which it is our purpose to discuss in the present section. 



Leaving out of account the multitude of strictly "littoral" or intertidal forms, we 

 meet with a considerable number of species which are limited to comparatively shallow 

 waters. An analysis or the depth records for all these species * reveals the occurrence 

 of many which were taken by us nearly or quite exclusively in waters less than 10 fathoms 

 deep. Many of these species, indeed, occur wholly or predominantly at depths of less 

 than 5 fathoms. A considerable number of such instances have been mentioned in the 

 discussions for the separate subdi\asions of the animal kingdom. A few of the commoner 

 species, among those dredged, which show a distinct preference for the shallower waters, 

 both in the Bay and the Sound, are: Pista palmata, P. intermedia, Amphithoe rubricata, 

 Biitium nigrum, Ceriihiopsis emersonii, Crcpidula convcxa, LaciDia puicola, Lyonsia 

 hyalina, and Mya arenaria. Now, an examination of the distribution charts for these 

 species shows that they were dredged chiefly, if not wholly, near shore. Some of them, 

 at least, are known to inhabit the intertidal zone as well. It is a noteworthy fact 

 fact that in some cases these species were dredged by the Fish Hawk, as well as by the 

 Phalarope, but only at such of the Fish Hawk stations as were situated in the neighbor- 

 hood of land. The depth at these points was often considerable, however (10 to 15 

 fathoms). Facts of this nature point to the conclusion that proximity to shore rather than 

 depth, as such, may be the factor concerned in determining the lower limit of distribu- 

 tion for species of this sort. Before deciding the point definitely, it would be necessary 

 to determine whether these "adlittoral" species occurred likewise on shoals at considera- 

 ble distances from the land. Unfortunately, we have no satisfactory data on this subject, 



o Petersen (1893, p. 445). declares the view of Semper that "every single species is affected by the temperature in a way char- 

 acteristic to itself alone is. I think, in the highest degree applicable to our marine animals. " 



f* Tables presenting these data were prepared for use in the preparation of this report, but they have not been included 

 herewith. 



