354 ' BULLETIN OF THE BUREAU OP FISHERIES. 



attachment as there was much variation in these. The Plymouth specimens were attached to gastropod 

 shells, the Canso specimens to shells and stones, the Grand Manan specimens to seaweed, the South Harps- 

 well specimens to shells and to rock, the Vineyard Haven specimens to piles of a bridge, the Tarpaulin 

 Cove specimens to shells, and the Beaufort specimens to shells. 



It is possible tliat the general habitat has something to do with size. At Vineyard Haven, where 

 the largest specimens were obtained, the colonies form encrusting masses completely covering the piles 

 from low-water point to a depth of several feet. That there is only one colony on each pile is indicated 

 by the fact that all the individuals on one pile are of the same sex. This bridge spans the narrow en- 

 trance to a large body of water known as Lagoon Pond. With every turn of the tide a strong current is 

 produced, a condition which is notably suitable for hydroid life, as an abundant food supply is assured. 

 If any other evidence were necessary it might be stated that a dozen species of hydroids were obtained 

 from these piles in less than half an hour. 



At South Harpswell the conditions were similar. The specimens were obtained at the site of an 

 old tide mill, where the current was strong enough to turn the mill wheel 8 hoius out of 12. Large 

 siu^aces of rock were covered with the colonies in much the same way that the piles were at Vineyard 

 Haven, though gastropod shells inhabited by hermit crabs were numerous also to provide a basis of 

 attachment. 



At Canso, the colonies were found along the shore at low water or on the bottom a short distance 

 below low water. As the Canso Peninsula projects so far into the Atlantic Ocean a tide current is run- 

 ning almost continually either into or out of Chedabucto Bay, past this point. Furthermore, as there is a 

 fringe of rocky islands and reefs surrounding the peninsula at a short distance out from shore, this tide 

 ciurent is broken up into innumerable small currents, some of which attain to a much greater velocity 

 as they move through the narrow passages. Here also an abundant food supply is assured. I do not 

 know the exact conditions at Grand Manan, but no place in the Bay of Fundy is likely to be without a 

 good supply of ciurent. It seems as though in all these cases the food supply was abundant, and large 

 specimens as well as large colonies were the result. 



In contradistinction to tliis, the small colonies were all found in quiet water. At Tarpaulin Cove 

 the colonies came up on the tangles used for collecting sea urchins or were obtained along the shore 

 at low tide. The cove serves as a good anchorage because of its sheltered waters. If the movement of 

 the water is slight the food supply of the hydroids can not be abundant. At Beaufort the specimens 

 were obtained \\'here the conditions were much similar to those at Tarpaulin Cove, at a depth of 10 or 12 

 feet in Bogne Sound, on sea-urchin ground, where the bottom is sandy with here and there lamellibranch 

 and other mollusk shells. There are 3 or 4 miles of shallow water before the open ocean is reached and 

 even the ocean is shallow for a long distance out. It is not surprising then that the colonies and the 

 individuals are even smaller here than at Tarpaulin Cove, for the latter is at least close to the deep weter 

 of Vineyard vSound. 



In many cases temperature appears to have much to do with the distribution of hydroids, and one 

 might suppose that the influence of temperatiu-e might account for the difference of size in this species, 

 since the larger specimens, in general, as far as this collection is concerned, are confined to the colder 

 waters and the smaller specimens the warmer. There is one difficult}' in the way of accepting such a 

 conclusion. The large specimens from Vineyard Haven were obtained but 7 or 8 miles from the very 

 small specimens at Tarpaulin Cove, and as there is direct water connection between the two places there 

 can be little difference in temperature. 



The variation in depth in the whole series is not enough to make any material difference in growth, 

 and it is hard to conceive of any other influence that might do so besides those mentioned. 



Difference in the food supply must be an important factor in producing this difference of growth 

 and it would seem, if one can judge from the specimens considered in this discussion, that it is the most 

 prominent factor. 



