184 PROCEEDINCx^ OF THE NATIONAL MUSEUM. vol.42. 



suspended in the water gradually sink and finally fall to the bottom, 

 leaving the liquid clear; a sign that their cilia have ceased to move. 

 At tliis moment they should be fixed, in order to retain their form; if 

 killed before completely narcotized, they will contract. The doses and 

 time intervals are : Every five minutes add from 1 to 3 drops of the 

 cocaine solution for each cubic centimeter of water in the tube. 

 After repeating this tliree times the narcotizing is usually finished. 

 To acquire practice, it is advisable to go through the operation two 

 or tliree times ^^dth a microscope at hand. Other animals, mainly 

 Entomostraca, that may be present do not suffer at all from the 

 narcotization, as they are also affected by the cocaine and sink to 

 the bottom about the same time. 



For fixation add to the tube 1 drop of the osmic acid mixture 

 for each cubic centimeter of its contents and mix? rapidly. This 

 amount should not be exceeded or the animals will be strongly 

 blackened. When they have settled to the bottom of the tube, 

 in 5 or 10 minutes at the most, the liquid is carefully decanted 

 and the tube refilled with water. This is repeated two or three 

 times in a few hours at intervals accordmg to convenience, finally 

 filling the tube with formalin solution, 1 part commercial formalin (40 

 per cent formaldehyde) to 9 parts distilled water. For transporta- 

 tion it is well to use quite a small tube. A slip of paper with neces- 

 sary data should be inclosed in each. 



To obtain the nonpelagic forms, aquatic plants (not temporarily 

 submerged plants), especially such as have finely divided leaves, 

 BatracTiium, Myriophyllum, Cerato'phyTlwm , and also floating plants, 

 as Lemna, Riccia, etc., should be brought home in a jar or tin can. 

 They should then be put into a glass jar with sufficient water to cover 

 them and left standing for two or tliree hours. All the animals 

 gradually come to the surface and collect on the illuminated side. 

 Direct sunlight should be avoided, as it liberates oxygen from the 

 plants and it is the lack of this that drives them to the surface. 



Quite an extensive fauna is to be found in mosses. Sphagnum, etc., 

 and as the only treatment necessary for this is simply to pick a few 

 handfuls of it and allow it to dry naturally, it is one of the easiest to 

 obtain. It should be collected from both wet and dry places The 

 BdeUoida are equally at home in both, and if Hepatics, such as 

 Jungermannia, FruUania, and others can be obtained, so much the 

 better. The surface layer of mud in dried-up pools should be scraped 

 off, well dried, but not heated, and finally stored m paper bags, if 

 possible sterilized, which, when once closed, should not again be 

 opened until arrival at the point of destination in order to avoid 

 contamination. The samples should be guarded against too high 

 temperature, laboratory fumes, etc., which are usually the reasons 

 why the animals fail to revive. 



