SCOTT, STUDY OF CHANGES IN MUSTELUS CANIS 



31 



tive to reductions in the density of the sea-water. Sheldon ('09) has con- 

 tributed ample evidence of the great sensitiveness of various parts of the 

 surface of its body to different chemical stimuli. The following instance 

 is cited merely for the purpose of indicating an interesting problem for 

 further investigation. At the New York Aquarium a tank about 250 cm. 

 long, 35 cm. wide and 10 cm. deep was filled with harbor water. A very 

 small Squalus acanthias about 35 cm. long, taken from harbor water, was 

 placed in this tank. The brackish water continued to flow in at one end, 

 while at the other end a stream of fresh water was run in. In a very 

 short time the dog-fish turned about and swam to the end receiving the 

 brackish water. It was then placed in the fresh water end, but swam 

 again into the brackish water. After a number of trials, it was clear that 

 the dog-fish was sensitive to the fresh water, as it persisted in seeking the 

 saltier end of the tank. The nasal pouches were then packed with ab- 

 sorbent cotton and vaseline. The fish was again placed at various places 

 in the tank, but swam about indifferently or remained stationary. Fur- 

 ther investigation of this problem was not possible on account of the lack 

 of proper facilities for experimenting with larger fishes. 



The greater number of species of fishes on exhibition at the New York 

 Aquarium are kept in the harbor water. What is the effect of such brack- 

 ish water on the osmotic pressure of the blood of the elasmobranchs sur- 

 viving it? Through the kindness of Dr. Townsend, the director, I was 

 furnished with a number of dog-fishes, Squalus acanthias, for the pur- 

 pose of securing an answer to the above question. At the time, the aver- 

 age specific gravity of the water was 1.015, which would correspond to a 

 A of about 1.00°. The freezing point of the blood of seven fishes was as 

 follows : 



Table XII. — Freezing point of the Mood of Squalus acanthias from New York 



harbor water 



No. 



Sex 



Length in cm. 



A of blood 



1 

 2 

 3 

 4 



5 

 6 



7 





56 

 58 

 38 

 43 

 41 

 61 

 61 



1.70 ° 



1.695 



1.70 



1.685 



1.695 



1.69 



1.66 



The average A of the seven fishes was 1.69°. This value is 0.18° 

 higher than the mean A of the blood of Mustelus in sea-water. At New 

 York, I was unable to get a sample of the blood of SqimJus as taken from 



