88 



FRESH-WATER BIOLOGY 



head of the camera, while a similar arrangement on the opposite 

 side of the box operates the mechanism which controls the expo- 

 sure. The operator wades and holds the box beneath the surface 

 of the water with only the upper part of the hood exposed. With 

 the right hand he focuses, with the left he makes the exposure. 



Jl 



FlG. 28. Floating water glass. For description FIG. 29. Water-tight metal box with plate-glass 

 see text. (From an original photograph.) front for enclosing a reflecting camera when used 



under water. For description see text. (From 

 an original photograph.) 



After each exposure the box must be opened to change the plate. 

 For details the reader should consult the literature cited. 



Means of Securing Collecting Apparatus 



The various types of commercial nets described may be had of dealers in 

 fishing nets. .The Simplex Net Company of Ithaca, N.Y., supplies ingenious 

 folding townets, plankton nets, and dip nets. The special apparatus mentioned 

 can be constructed by any skilled mechanic under direction. 



IMPORTANT REFERENCES ON APPARATUS AND METHODS 



APSTEIN, C. 1896. (See list in Chapter I.) 



BIRGE, E. A. 1895. (See list in Chapter I.) 



FORDYCE, CHAS. 1898. A New Plankton Pump. Proc. and Coll. Neb. 

 State Hist. Soc., 2: 293-296. 



HELLAND-HANSEN, B. 1912. The Ocean Waters, an Introduction to Physi- 

 cal Oceanography. I. General Part (Methods). Int. Rev. ges. Hydrob. 

 u. Hydrog., Hydrogr. Suppl., i. ser., Heft 2. 



HENSEN, V. (See list in Chapter I.) 



