160 Puget Sound Marine Sta. Puh. Vol. 1, No. 14 



which light sufficient to affect plates sensitized with silver chloride pene- 

 trates, while its lower limit is about the depth to which sufficient light 

 jjcnetrates to affect plates sensitized with silver iodobromide. The pres- 

 sure ranges from 10-20 atmospheres. No material used in the experi- 

 ments was obtained from this depth from any other locality than the 

 narrow area studied by Miss Perry {plate 29). 



3. Methods of Collecting and Keeping Material 



With the exception of specimens of three or four species obtained 

 at stations A, B, C and D, the animals used in the experiments were 

 dredged or secured between the tide lines in a small area north of 

 Brown Island (plate 29). A regular Challenger dredge was commonly 

 used; though at times a large Puget Sound trawl was used, especially 

 where the bottom was known to be rocky. The Puget Sound trawl is 

 apparently a local invention similar to the usual beam trawl but with 

 a heavy iron bar from 1-4 inches from the level of the runners. The rig 

 is not very effective and according to fishermen is being replaced by the 

 usual type of beam trawl with a lead line instead of the bar. 



Collecting was usually carried on in the forenoon, and experiments 

 performed in the afternoon of the same day. Material from deep water 

 was usually kept in a float car. The car had several compartments and 

 was so constructed as to be towed out alongside the vessel. It was cov- 

 ered with a piece of heavy canvas. Several washtubs were also used 

 and the water changed often. Material was kept in the float car 

 until used. According to the experiments of Petersen (18), a dredge se- 

 cures only about three or four percent of the animals on the surface over 

 Avhich it is dragged. They took some animals in the bottom sampler 

 that did not appear in the dredging and vice-versa. Miss Perry's table 

 at the end of this article shows the relative abundance of the animals ob- 

 tained in the dredge but can not represent the true population of the 

 bottom. 



4. Water Supply 



The salt water supply of the station is pumped chiefly in the morn- 

 ing and evening from the bay immediately adjacent at about 4 feet below 

 mean tide. It was stored in a wooden tank. The temperature rises from 

 11° to 14° C. on warm days. Differences in the character of the water 

 from different points near the station were not wanting. Table 1 brings 

 out some of these differences. 



