214 J. MURRAY ON GASTROTRICHA. 



and possess only one vibrating cell corresponding to the series- 

 of flame-cells of Rotifera ; there is no contractile vesicle, and the 

 canals open independently on the ventral side and have no 

 connection with the intestine. 



While the eggs are frequently conspicuous, and their develop- 

 ment may be conveniently studied, the sexual system is little 

 known. Zelinka distinguishes paired ovaries. If the supposed 

 male organs are such the Gastrotricha are hermaphrodite. 



Zelinka recognises in the alimentary canal the following parts : 

 mouth, oesophagus, stomach, intestine with rectum and anus. 



There is a well-developed muscular system, and the brain and 

 nervous system are similar to those of the Rotifera. 



Haunts and Habits. 



The Gastrotricha are found mainly in ponds, oftenest among 

 the bottom sediment or vegetation. They rarely occur on mosses, 

 except the permanently moist aquatic kinds. A few (at least 

 one species, C. marinus) live in the sea. 



They are much less common, even in ponds, than the 

 Rotifers and Water-bears. You cannot go out to collect 

 assured of getting some you must trust to casual occurrences 

 when studying other things. 



There are no special methods of collecting them. They will 

 occur among your Rotifers, but not if you collect in clear, open 

 water. Perhaps the likeliest means to obtain some is to wash 

 aquatic weeds Myriophyllum, Fontinalis, Lemna, etc. 



If you wish to preserve them it can easily be done. As they 

 are not contractile, they can be killed without previously 

 narcotising by osmic acid, when they retain the natural shape.. 

 They can be mounted in fluid cells by Rousselet's method, but 

 formalin of the strength used for Rotifers is not a suitable 

 medium, as it produces subsequent distortion. Some better 

 medium has yet to be found. 



They appear to have only one habit, that of eating. They 

 ar; always in motion, some slowly, some quickly, and always 

 seem to be nosing for food. Yet they are not greedy eaters, but 

 pick daintily here and there. As they creep along over the weeds 

 they give the impression of active intelligence proportioned to- 

 their needs. 



