THE SHIP AND ITS EQUIPMENT ^3 



dredging, the time required for dredging depending, of course, 

 upon the nature of the bottom. 



The joint labours of Agassiz and Sigsbee led to a great 



Fig. II.— The "Challenger" Trawl. Fig. 12.— Sigsbee's Trawl. (From Sigsbee.) 



improvement in the appliances. Previously the dredges had 

 ploughed into the ocean floor (Fig. 10, a), but the one employed 

 by Sigsbee (Fig. 10, d) was believed to have skimmed over it, 

 and so collected the animals which lived upon the surface, 

 sweeping them up from a wide extent of ground. Both kinds 



D 



