PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS. 221 



instance, as Echinoderm larva), it is essential that the boat should be 

 rowed so slowly that the net may move gently through the water, so as to 

 avoid crushing its soft contents against its sides. Those of firmer struc- 

 ture (such as the Entomostraca) on the other hand, may be obtained by 

 the use of a Tow-net attached to the stern of a sailing vessel, or even of 

 a steamer, in much more rapid motion. 1 When this method is employed, 

 it will be found advantageous to make the net of conical form, and to 

 attach to its deepest part a wide-mouthed bottle, which may be prevented 

 from sinking too deeply by suspending it from a cork float: into this 

 bottle many of the minute Animals caught by the net will be carried by 

 the current produced by the motion of the vessel through the water, and 

 they will be thus removed from liability to injury. It will also be useful 

 to attach to the ring an inner net, the cone of which, more obtuse than 

 that of the outer, is cut off at some little distance from the apex; this 

 serves as a kind of valve, to prevent objects once caught from being 

 washed out again. The net is to be drawn in from time to time, and the 

 bottle to be thrust up through the hole in the inner cone; and its contents 

 being transferred to a screw-capped bottle for examination, the net may 

 be again immersed. This form of net, however, is less suitable for the 

 most delicate objects, than the simple Stick-net used in the manner just 

 described. The Microscopist on a visit to the seaside, who prefers a 

 quiet row in tranquil waters to the trouble (and occasional malaise) of 

 dredging, will find in the collection of floating Animals by the careful 

 use of the Stick-net or Tow-net a never-ending source of interesting 

 occupation. 



1 In the 'Challenger' Expedition, Tow-nets were almost constantly kept in use, 

 not only at the surface, but at various depths beneath it; being attached to a 

 line which was made to hang vertically in the water by the attachment of heavy 

 weights at its extremity. The collections thus made showed the enormous 

 amount of minute Animal life pervading the upper waters of the Ocean. 



