6 C. McLEAN FRASER 



to bring a good food supply to the animals that are near enough 

 to reap the benefit. In the San Juan Archipelago the conditions 

 are very much as those already described. The shores of the va- 

 rious islands are in general not very well adapted to collecting, 

 though there are some favored spots. The numerous channels 

 between the islands give a variety of current and plenty of inter- 

 change to make good feeding grounds for such forms as Hydroids. 

 As the Archipelago is in the direct path of the current through 

 the Strait of Juan de Fuca, these conditions are accentuated. 

 The base for work in this vicinity is at Friday Harbor, on the 

 Eastern or sheltered side of San Juan Island, at which there is 

 now a regular Biological Station under the direction of Prof. T. 

 Kincaid of the University of Washington. 



My thanks are especially due to Prof. C. C. Nutting, who has 

 given so much advice and assistance and supplied so many con- 

 veniences for advancing the work. The list of papers available 

 for consultation has been extended through the kindness of the 

 Librarian of the John Crerar Library, Chicago, who, through Mr. 

 M. G. "Wyer, the University Librarian, loaned some rare and im- 

 portant papers. I wish also to express my obligation to Rev. Gr. 

 W. Taylor, Prof. John ]\Iacoun and Dr. A. G. Huntsman for col- 

 lections of material, to Prof. Josephine E. Tilden and Prof. Con- 

 way Mac]\Iillan for their courtesy and assistance at the Minnesota 

 Seaside Station, and to my wife who has contributed to the work 

 by making the pen drawings for the plates from camera-lucida 

 drawings supplied. 



GEOGRAPHIC DISTRIBUTION 



In 1876 Dr. S. F. Clark reported 24 species of Hydroids from 

 the Pacific Coast, south of Vancouver Island and later in the same 

 year 42 species from Alaskan waters. Taking these reports as a 

 basis he concluded that since he found only one species, Lafoea 

 dumosa, in the two regions, there must be a distinct break in dis- 

 tribution between the two regions. Investigations since that time 

 have shown that no such generalization should be made on so 

 small an amount of data. The more the group is studied and the 

 greater the number of locations for examination included, the 

 more reason there is for believing that there are no sudden, nor 

 even comparatively sudden, breaks in distribution along the en- 

 tire West Coast, though naturally certain species gradually dis- 



