THE TOW-NET. 



129 



The tow-net, Fig. 1 1 5, is of great use in collecting marine, 

 and even river or lake objects. It is made of fine but strong 

 muslin, tied at the large end round a wooden hoop, while 

 the nethermost extremity is secured round a small wide- 

 mouthed bottle, so that the more deli- 

 cate organisms may find their way 

 into it, and so be out of the way of 

 the currents caused by the passage 

 of the net through the water. 



The tow-net, as illustrated, is fur- 

 nished with an interior net, which, 

 acting as a valve, prevents the escape 

 of organisms which have once been 

 enclosed. 



Aquatic organisms, whether animal 

 or vegetable, are met with in all kinds 

 of water ; even the tap water supplied 

 by some of our corporations is ex- 

 tremely rich in specimens, while in 

 clean ponds the collector will not fail 

 to find a host of treasures ; in impure 

 streams and pools, containing sewage 

 and other decomposing matters, only 

 such common animalcula as Para- 

 mecium aurelia are to be found. 

 Other objects are fixed upon stones 

 and weeds under water, and little 

 pieces of dead stick are often found 

 covered with interesting objects. 



When the water is not rich in specimens, it may be 

 necessary to concentrate them by straining off the super- 

 fluous water, which may be effected by using the filter 

 shown in Fig. 1 16. It consists of two small funnels passing 

 through a cork as shown in the figure, the one which is 



K 



FIG. 115. 



