STRUCTURE OF PLUMATELLA. 167 



act directly upon them,* and without the previous 

 or simultaneous production of sensation or con- 

 sciousness. 



There are many other genera and species of fresh- 

 water polyzoa besides the Plumatella repens^ and 

 they are found attached to sticks, stones, or leaves, 

 generally to the under surface of the latter. 

 They are all objects of great interest and beauty, 

 which, whatever their diversity, conform sufficiently 

 to one type that the student who has observed one, 

 will easily recognise the zoological position of another. 

 They should be viewed by transmitted and by re- 

 flected light, and by dark-ground illumination, which 

 produces very beautiful effects. To observe them in 

 the performance of their functions, they require 

 more room than the live-box can afford, but are 

 well shewn in the glass trough, whose moveable 

 diaphragm enables them to be brought near enough 

 to the object glass, for the use of a power of al)out 

 sixty linear for general purposes, and of from one 

 to two hundred for the examination of particular 

 parts. For a more detailed examination dissection 

 must be employed, but all that Ave have mentioned 

 can be seen without injury to the living animal, 

 if specimens are kept till new cells are formed in 

 water, which does not contain enough dirt to render 

 their integuments opaque. 



* Carpenter's Manual of Physiology, p. 212. 



