vol. i.i Torreij. — Hydroida of the Pacific Coast. 39 



free end is connected by a much attenuated stalk to the place of 

 origin. It finally turns outward, investing itself with perisarc 

 and may attain to the length of an inch, penetrating between and 

 adhering to sand grains. The longest processes are usually 

 nothing but perisarc, the attenuated coeuosarc having disappeared. 



The characteristic attitudes of the expanded hydroid are some- 

 what different from those of G.pendula. It is oftenest perfectly 

 erect, in quiet water, the plane of the tentacles being slightly 

 tilted from the horizontal. It may bend downward, however, in 

 which case the arching includes the greater part of the stem. I 

 have never seen it assume the pendulous attitude shown in 

 Agassiz's figures of C. pendula. 



Orientation. A few simple experiments demonstrated that 

 the erect posture of the stem was assumed in response to a 

 geotropic stimulus. To determine relatively the specific gravity 

 of different parts of the polyp, the basal tufts of sand-incrusted 

 filaments were cut from several polyps and the latter were placed 

 in an aquarium. They sank directly to the bottom, distal 

 (hydranth) end foremost. Then several other polyps, together 

 with two polyps with proximal filaments removed, were put into 

 a jar filled with water so that all but a small bubble of ah- was 

 excluded when sealed. When the rooted polyps had assumed 

 erect postures the jar was transferred to a dark closet and tilted 

 at an angle of 45°, the polyps remaining parallel to the sides of 

 the jar. In an hour all the polyps had become erect. The jar 

 was righted, and within another hour the polyps had oriented 

 themselves again in line with the pull of gravity. The polyps 

 without basal filaments did not change their position materially 

 during the whole experiment, without doubt because they lacked 

 a proximal point of support. 



There was no difference in the result when the experiment was 

 performed in the light or in darkness. To determine whether 

 light exercised a directive influence, several polyps were exposed 

 before a window, so screened that the light came from one 

 direction only. At the end of three hours, no effect on their 

 attitudes was visible. Light thus appears to be without influence 

 as an orienting factor, and the following experiment was per- 

 formed in the day light. 



