54 



HA RD WICKE'S SCIENCE- G OS SIP. 



one piece as a double cone, one seam of the smaller 

 being left uncompleted, so that, when a net is worn 

 out, all that is necessary is to turn this small cone 

 over the ring, close the seam, and sew lightly together 

 below the ring. The lower calico portion outlasts 

 several changes of muslin. Three short lengths of 

 cod-line are secured to equidistant points on the 

 circumference of the ring and knotted together into 

 a loop, about three or four feet from the net, which 

 serves to bend on a piece of log-line, by means of 

 which the net is hung in the water. 



All being now " ready for sea," a piece of fine 

 muslin is stretched over the large end of the glass 

 tube, and tied behind the shoulder or rim with a 

 piece of fine string, the ends of which are left a few 

 inches long. The small end of the glass tube is now 

 introduced, through the cork, into the calico tube ; 

 and, unless^ very tightly held, for extra security, the 

 free ends of the string used to lash on the muslin 

 are knotted together and tied behind the cork. Then, 

 by means of the log-line, the whole is lowered over- 

 board into the tide. 



Fig- 37 shows the tube in place ready for use ; 

 Fig. 38, a long section of the entire apparatus. 



And now as to the method of using it. By far 

 the best plan is to make it fast to a small buoy in a 

 place as little frequented by shipping as possible. 

 For this purpose a small keg or beaker, anchored by 

 means of a heavy stone, is sufficient, or, in harbours, 

 advantage may be taken of the large buoys used to 

 mark out the channels. Of course, when used from 

 a rowing-boat, nothing more is necessary than to 

 bring this to an anchor in a suitable situation, or to 

 row her gently so as to make her just hold her own 

 against the tide ; but in a ship at anchor it is very 

 difficult to find a situation where the net can be kept 

 clear of the rubbish that is continually being thrown 

 overboard. 



The "Investigator," the vessel belonging to the 

 Indian Marine Survey, is a paddler, and by rigging 

 out a 20-ft. bamboo from the paddle-box, one is 

 enabled to get pretty clean hauls ; but in a screw- 

 ship a much longer spar would be required. Perhaps, 

 all considered, the best situation on shipboard is from 

 the bowsprit end. But, in this case, to prevent the 

 net from being carried aft against the bows, a 141b. 

 sounding lead must be made fast to the line, about a 

 yard from the net, as in Fig. 39. In this situation 

 none of the ship's rubbish can possibly get into the 

 net ; but to trust its application, and more especially 

 the operation of drawing it, to one of the crew, is a 

 somewhat hazardous experiment ; and it requires a 

 certain amount of nautical experience to enable one 

 to go out on the spar with confidence. Moreover, in 

 a passenger ship, one would certainly "get one's toes 

 chalked," and have to "pay one's footing" for the 

 exploit ; but, these difficulties overcome, the perfect 

 cleanness of the haul well repays the small extra 

 trouble and, perchance, expense. 



In withdrawing the net from the water, care should 

 be taken not to do so too suddenly, as, unless raised 

 slowly, so as to give time for the water to run out 

 through the interstices of the muslin, the weight of 

 water taken up is apt to burst the net. Before 

 finally withdrawing the tube part from the water the 

 ring should be once or twice dipped, so as to take up 

 a little water, which washes through the bag and 

 carries anything that may be left adhering to the 

 muslin on into the tube. As soon as the net has 

 been hauled aboard, the tube end should at once be 

 immersed in a bucket of sea- water ; and, holding it in 

 this position, the bag part is removed by drawing off 

 the cork ring. Now raise the tube until only about 

 half or three-quarters of an inch of water is left in 

 the large end. Insert a well-fitting indiarubber cork 

 into the small end, and smartly invert the tube ; 

 after which the muslin may be removed from the 

 large end. 



On holding the tube up to the light it will, as a 

 rule, be found to completely swarm with organisms 

 of the most varied descriptions ; and any individual 

 that may be especially remarked may be captured at 

 this stage by means of a section-lifter provided with 

 a very long handle, and put aside. If, however, as 

 is most commonly the case, the crowd is so dense 

 that it is impossible to follow the motions of any 

 individual specimen, the catch must be examined in 

 successive small portions, in a large flat glass cell 

 under the simple microscope. For work on ship- 

 board, on account of the motion, it is necessary to 

 have these cells deep in proportion to the depth of 

 fluid they are intended to contain : 3 X 2 X f inches 

 is a useful size. 



(To be continued.) 



ON THE VARIATION AND CONTINENTAL 

 DISTRIBUTION OF THE BRITISH SLUGS. 



By J. W. Williams, D.Sc, &c 



TO me the slugs, with their near relatives the 

 snails, stand as the greatest living protests to 

 the promulgation of Linne of the stability of species. 

 In one of his occasional addresses, contained in the 

 " Amoenitates Academica:," and entitled, " Oratiode 

 tellure habitabili," the great Swede says : " Initio 

 rerum ex omni specie viventium unicum sexus par 

 fuisse creatum suadet ratio ;" and this maxim held its 

 ground until Cuvier followed him, and with a tincture 

 of philosophy questioned the persistence of species ; 

 and the observations and logical deductions made by 

 naturalists since his time, such as Geoffrey St. Hilaire, 

 Lamarck, Oken, Goethe, Wallace, Darwin, Haeckel, 

 and others, have furnished data to conclusively nega- 

 tive any adherence to the old doctrine of Linnaeus. 

 To-day in our own country the conchologists are 



