DltKDGING AT OBAN. 85 



most when the dredije is lowered to the bottom. The present tangles 

 at the bottom of the dredge-net to be retained as an additional pro- 

 vision, and the new tan^jle-bar to be made as nuic-h wider tlnm the pre- 

 sent dredfie-net as may be practicable for convenient liandlinti on deck. 



In the " Challeni^er " Dred^'inj^ it is wcrthy of note that the <;reater 

 portion of the work was done witli a wide tnncl-itct carried by a trans- 

 verse beam that was as much as 18ft. in width with 20ft. len<^th of net ; 

 and this was found so superior in results to the regular dredge-net of 

 ■l.tft. width and 4Aft. length, that the trawl-net was used for depths 

 even as great as 3,000 fathoms, or 3| miles. The two ends of the 

 trawl-beam were carried about a foot clear above the surface of the 

 ground by an iron-runner fixed to each end (like sledge-runners). 



The trawl-net has an objection in the rather longer time required 

 for sinking it to the bottom, and it is not so suitable for rocky or 

 uneven ground as the narrow dredge ; but it was used almost con- 

 stantly during the latter part of the voyage of the " Challenger." In 

 the deep-sea dredging (generally about three miles depth), the time 

 required for lowering and hauling np the dredge was so great that only 

 a single dredging operation could be effected in each day ; the lowering 

 of the dredge took about 8 hours, it was then allowed to remain at 

 the bottom from 1^ to 2 hours, and 4 to 5 hours was taken for hauling 

 up, the average rate of hauling up being 1ft. per second, or 10 fathoms 

 per minute. The total number of dredgings effected in the 3^ years 

 that the " Challenger" voyage lasted was consequently not more than 

 504, these being nearly all deep-sea dredgings, extending to an extreme 

 depth of 3.950 fathoms, or 4§ miles. 



In future dredging excursions of the Society it appears also desir- 

 able to consider the employment of a small-sized dredge in addition to 

 the ordinary dredge, and so small in size that it can be hauled in 

 readily by a single hand, and can be quickly and conveniently used as 

 a trial dredge without involving the delay and labour of lowering and 

 raising the large dredge. Such a dredge, of only seven inches width, 

 and requiring a rope only as large as a common lead pencil, has been 

 very successfulh' used down to a depth as great as 60 fathoms by Mr. 

 David Robertson, of Glasgow, in his important dredgings for Foramin- 

 ifera on the coasts of Scotland and Norway. 



In reference to the preserving of specimens, it is very desirable that 

 on future occasions (as pointed out in the Report on the Penuatulida 

 from Oban) some few specimens of each object —fragments will suffice 

 — should be preserved at once in spirit directly they are captured, so as 

 to be in good and natural histological condition for subsequent detailed 

 examination with the mici'oscope. The want of such preparations has 

 been specially experienced in the microscopic examination of the 

 Pennatulida specimens for determining difficult points of histological 

 structure ; the change of circumstances in the exposure of a deep- 

 water object, even for a short time, to the higher temperature, 

 diminished pressure, and greater light of surface water, being un- 

 favourable to an accurate preservation of the microscopic details in 

 animal structure. 



