MOVEMENTS OF HERRING AND OTHER MARINE FISHES. 327 



28.6 c.c. per 1, of bound carbon dioxide. There was a deficiency 

 of oxygen and what was present was probably due to leaky pipes. 

 It was only 0.5 c.c. per liter. It contained a large excess of some 

 odorless gas which escaped in bubbles and was probably nitrogen. 

 This water was aerated by running it over a board 420 cm. long, 

 into the siphon bucket. This reduced the gas in excess to air 

 saturation and raised the oxygen to 4.8 c.c. per liter. 



In the experimental tank the difference between the density 

 of the fresh and salt water was so great that the fresh extended 

 nearly to the opposite end at the top with very little mixing and 

 the salt water occupied a corresponding place on the bottom. 

 Thus there was a sharp gradient from top to bottom, but a very 

 imperfect one from end to end. To avoid this siphons were 

 inserted which withdrew water from each side near the bottom 

 at a point one third the length from the salt end and from near 

 the top at the same distance from the fresh end. This was found 

 not to remedy the difficulty sufficiently and so a screen incline 

 which extended from bottom at the salt end to the height of 

 8.5 cm. at the fresh end. Above this was another screen which 

 was 8.5 cm. at the salt end, and which ran up to the surface of 

 the water at the fresh end. This enclosed the fish in an inclined 

 cage 8.5 cm. deep at the salt water end and 5.0 cm. deep at the 

 fresh end. The fish moved back and forth in this at a distance 

 of about 4 cm. from the lower screen. The gradient of salinity 

 between the acid sea water and the alkaline fresh water was 

 essentially as perfect as shown in the accompanying Fig. i. By 



4,41 4.37 '^'^4 



7.05 

 7.10 



A^l^ 1" ^ 



,10.56 — t^ 



--"'?---»- r 





6.45. 



10.53 9.59 7.19 



Fig. I. 

 Fig. I. Showing the distribution of salinity in terms of grams of chlorine per 1. 

 in Roman and oxygen content in c.c. per 1. in italics; Al, alkaline; N, neutral; Ac, 

 acid. 



consulting this figure it will be seen that the oxygen content 

 was essentially the same throughout. The salinity corresponded 

 to 10.561 grams of chlorine in the salt water end to 6.45 grams 

 in the fresh water end. The acidity to phenolphthalein reached 



