284 



THE AMERICAN NATURALIST 



[Vol. LVI 



occurred. Whether the injury to the arm was the source of the 

 change is not apparent. 



It will be seen, therefore, from the above account that both 

 descriptions of the tube-feet arrangement are correct, but that 

 the one usually given in text-books (Type I) is by far the more 

 common; furthermore, that the one type may change to the 

 other with no apparent structural reasons for the transforma- 



The facts here presented furnish, I believe, a complete explana- 

 tion of the difference in the laboratory accounts as given by 

 different teachers. 



Egbert H. Bo wen 



Marine Biological Laboratory, 



THE MICEO-FILTER FOR MINUTE FLAGELLATES 



It is frequently desirable during the study of the minuter 

 protozoa, and especially of the small flagellates, to concentrate 

 the organisms. This the writer has been able to do in a very 

 simple and satisfactory manner by means of the device shown 

 in Fig. 1, which may be called the micro-filter ; a name applied not 

 only because of its office, but also because of the minute piece 

 of filter-paper used. 



The contrivance consists of a standard, either of wood or of 

 metal, which supports a burette tube, a minute circle of filter- 

 paper, and a vessel beneath. The water containing the protozoa 

 to be eoncentrated is introduced into the burette from above, 

 by means of a funnel, and the pinch cock (0) opened sufficiently 

 to allow the liquid to drop into the small funnel or circle of 

 filter-paper beneath (P). The filter is supported by means of 

 stout copper wire. The flow of water from the burette can be 

 nicely regulated by means of the pinch cock, which, to give the 

 best results, should be of the screw variety. The water drops 

 through a glass tube, drawn out into a fine point (T). It was 

 found convenient to have several of these tips of different diam- 



Considerable experimentation is necessary before the exact 

 balance between the flow of water from the burette and that 

 from the base of the filter-paper funnel can be secured. When 

 this balance is reached, the burette is filled and the water allowed 



