ON COLLECTING SHELLS. 



139 



captured alive, its movements should be watched m a vessel of 

 sea-water, to see whether it has the power of rising and sinking 

 at will ; its mode of swimming, and position during these move- 

 ments, and when at rest. The chambered shell should be opened 

 under water, to ascertain if it contain a gas, the nature of wh-'ch 

 should, if possible, be made out. The pearly nautilus requires 

 the same observations, which would be attended with more 

 precision and facility from its larger size." (Owen.)* 



The towinri-netVLQQ^ by Mr. McGillivray " consisted of a bag 

 of hunting (used for flags) 2 feet deep, the mouth of which was 

 sewn round a wooden hoop 14 inches in diameter ; three pieces 

 of cord, 1| foot long, were secured to the hoop at equal inter- 

 vals and had their ends tied together. When in use, the net 

 was towed astern, clear of the ship's wake, by a stout cord 

 secured to one of the quarter-boats, or held in the hand. The 

 scope of the line required was regulated by the speed of the vessel 

 at the time, and the amount of strain caused by the partially 

 submerged net." f 



Trawling. — Mr. John "W. Woodall,of Scarbro', has kindly fur- 



Fig. 32. A Trawl-net. A. Side view; B. Net in op ration ; C. Plan. 



nishedthe following sketches and particulars : — " B, Fig. 32, ig 

 intended to represent a trawl-net at work on the bottom of the sea. 



» Admiraltj' Manual of Scientific Inquiry. 8vo. Lend, 1849. 

 t Voyage of H.M.S. Mattlesnake, vol i. p. 27. 



