14 Marine Invertebrates 



tion for the wood and is perfectly harmless even to the most delicate 

 forms.* It may be constructed according to the desired size and shape. 

 So-called "white wood" (trade name) untreated in any way but ab- 

 solutely dry should be used. All wooden parts must be painted sep- 

 arately before they are put together and a second coat of paint (No. 24 

 Scotch heater, manufactured by Billing and Chapin Co., N. Y.) is ap- 

 plied after the aquarium is assembled. To prevent cracking of the 

 wood, the aquaria must be kept moist all the time. 'For mounting the 

 glass a type of putty containing no toxic substances and remaining plastic 

 for a long period should be used. Putties that harden quickly should 

 be avoided for they may exert uneven pressure on the glass wall and 

 cause it to crack.** 



For more critical experimental work in which a complete elimination 

 of foreign substances is important, only glass containers should be used. 

 All kinds of glassware found on the market may be used for the cul- 

 tivation of marine forms. Fruit jars, battery jars, precipitating cylinders 

 and more expensive pyrex containers of various shapes and dimensions 

 may be suitable depending upon the requirements of the investigator. If 

 running seawater is not needed small and medium-sized organisms may 

 be kept successfully in ordinary finger bowls, 4 inches in diameter, or 

 in so-called specimen dishes, 7 inches in diameter. These dishes made 

 of heavy glass may be placed one on top of another and are very easy to 

 handle. 



For delicate physiological work, as for instance the experiments on 

 fertilization, only the best grade of glass or even quartz should be used. 

 A cheap type of glassware is usually more or less discolored and of 

 uneven thickness. These defects make it unsuitable for photography or 

 for the observation of organisms through a low powered microscope. 

 For these purposes a better type of glassware with parallel walls should 

 be selected. For the cultivation of diatoms, other marine unicellular 

 algae, and flagellates small round flasks are usually used. 



Success in cultivating marine organisms depends not so much on the 

 shape and size of the container used as on the cleanliness of the glass. 

 This fact cannot be overemphasized, for many observations have been 

 ruined because of the contamination of the glass by toxic substances the 

 presence of which was not suspected. It is a safe rule in experimenting 

 with living forms never to use glassware which has been previously em- 



* If it is intended to keep the organisms under observation, a glass walled aquarium 

 should be used. 



** The following recipe developed by Prof. Petrunkevitch was found to be excellent: 

 place a portion of spar varnish in a can, stir in screened Portland cement until quite 

 thick. Do not add more cement until the combined mass has stood one or two hours. 

 As the mixture thickens in standing, the consistency should be nearly that of putty. Keep 

 in tightly covered cans. 



