vol.l] Tor raj. — Hydroida of the Pacific Coast. 57 



It is not an unusual thing to see the branches of 0. conimis- 

 suralis — and the associated C. pacifiea and G. clarki — grown out 

 into tendril-like processes. These appear so constantly in 

 colonies confined in aquaria, or growing in dirty water or under 

 other unfavorable circumstances, that there can be no doubt of a 

 causal relation between their appearance and external conditions, 

 though the definite cause is as yet obscure. The processes are 

 usually attenuated, with very thin perisarc, and grow rapidly: 

 2 to 3.5 mm. in 24 hours. They may be ringed at intervals or 

 smooth, and may be terminated by hydranths of proportionate 

 size. They often behave like, stolons. When one comes in 

 contact with a solid substratum, it may cling to it. So long as 

 it is in contact with the substratum it does not develop rings or 

 end in a hydranth. The stimulus of contact, however,' is not 

 necessary to the transformation of these processes. While free 

 they may not only remain smooth but give rise to buds at right 

 angles to their own axes, just as attached stolons do. The 

 growing point of each develops rapidly, while the hydrocaulus 

 behind thins out and may degenerate completely. In this way a 

 given area may be quickly occupied by colonies which have 

 arisen non-sexually from a single one sexually produced. Here 

 is a function of possibly adaptive value, its activity dependent, 

 however, on appropriate external conditions. 



It is apparent that the attenuated branches of these species 

 have no phylogenetic significance, being explicable on physio- 

 logical grounds. I have little doubt that the "long filiform 

 tendrils" described by Calkins in 0. surcularis, which bear "in 

 some cases, one or two hydrothecae" are in the same category 

 and have no value as specific characters. 



Obelia dichotoma (Linn.). 



Sertularia dichotoma, Linnaeus, Syst. Nat., 1756, X ed, p. 812. 

 Obelia dichotoma, Schulze, Nordsee Exp., Hydr., 1872, p. 129. 

 Calkins, Proc. Boat. Soo. N. H., 1899, XXVIII, p. 356. 



Distribution. San Pedro to Coronados Is., Cal. Puget 

 Sound (Calkius). Sitka, Berg Inlet and Orca, Al. (Nutting). 

 British coasts (Hincks). Heligoland (Schulze). Eastern U. S. 



(Nutting). 



