COLLECTING 529 



water it contains to drain through it ; and should then be turned 

 inside out and moved about in a bucket of water carried in the 

 boat, so that any minute organisms adhering to it may be washed 

 off before it is again immersed. It is by this simple method that 

 marine animalcules, the living forms of Radiolaria, the smaller 

 Medusa ids (with their allies Beroe and Cydippe), Xoctiluca, the 

 free-swimming larvae of Echinodermata, some of the most curious 

 of the Tunicata, the larvae of Mollusca, Turbellaria, and Annelida, 

 some curious adult forms of these classes, Entomostraca, and the 

 larvae of higher Crustacea, are obtained by the naturalist ; and 

 the great increase in our knowledge of these forms which has been 

 gained within recent years is mainly due to the assiduous use 

 which has been made of it by qualified observers. It is important 

 to bear in mind that, for the collection of all the more delicate of 

 the organisms just named (such, for instance, as echinoderm larvae), 

 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 structure (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, w r ho 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. 



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