EIGHTH ANNUAL REPORT. 81 



the greatest value in nature study, in arousing the interest of the 

 pupils, and are vastly more instructive than illustrations in the 

 books. 



In response to numerous requests from biology teachers for as- 

 sistance in establishing small study aquaria in the school-rooms, 

 an expert from the Aquarium was detailed to visit all schools 

 making application, and give the teachers practical instruction in 

 maintaining these valuable aids to nature study. The coopera- 

 tion of the Board of Education was secured ; the Board agreeing 

 to supply the teachers with aquarium jars and transport to the 

 schools the necessary supply of sea-water. The collections for 

 these aquaria are furnished free from the surplus stock at the 

 New York Aquarium. About ioo small aquaria have already 

 been placed in schools, both teachers and pupils taking great in- 

 terest in them. The number is being steadily increased as teach- 

 ers make application for them. This work is in the hands of Mr. 

 L. B. Spencer, of the Aquarium. 



A small library of works on marine and aquatic life has been 

 acquired for office purposes, and for the use of teachers and oth- 

 ers studying the collections. 



DENSITY OBSERVATIONS AT THE AQUARIUM. 



The remarkable conditions under which sea fishes have always 

 been kept at the Aquarium rendered it desirable that regular ob- 

 servations be made on the density of the water. Ocean salinome- 

 ters were secured and the results of a year's observations show 

 some very interesting conditions, especially with respect to fishes 

 from the Bermuda Islands, where ocean densities are probably 

 at their highest. While it is a fact that some of these fishes live 

 in the Aquarium for months, and even for years, the majority of 

 the species in each collection brought from that region do not 

 survive many weeks. 



Injured fishes, that have been bruised at the time of captivity 

 and during transportation, frequently heal in a short time if the 

 density of the water happens to be at its highest when they arrive 

 at the Aquarium. Should the density be low, they are apt to die 

 much sooner, as their injuries do not heal under such conditions. 

 Should the Hudson River be high when new fishes, either tropical 

 or local, are received, the mortality is apt to be greater than when 

 the river is low. The highest death-rate among the sea fishes 

 that the Aquarium has had for some time followed the heavy 

 floods of the past summer. During the winter and spring the 

 densities are much lower than in summer. 



Sea fishes living in water of low density are affected in other 



