236 COLLECTION OF AQUATIC OBJECTS. 



look for. In the present place, general directions only will be 

 given ; the particular details relating to the several groups being 

 reserved for the account to be hereafter given of each. 



176. Of the Microscopic organisms in question, those which 

 inhabit fresh water must be sought for in pools, ditches, or 

 streams, through which some of them freely move ; whilst others 

 attach themselves to the stems and leaves of aquatic Plants, or 

 even to pieces of stick or decaying leaves, &c, tbat may be floating 

 on the surface or submerged beneath it ; while others, again, are to 

 be sought for in the muddy sediments at the bottom. Of those 

 which have the power of free motion, some keep near the surface, 

 whilst others swim in the deeper waters ; but the situation of 

 many depends entirely upon the light, since they rise to the 

 surface in sunshine, and subside again afterwards. The Collector 

 will therefore require a means of obtaining samples of water at 

 different depths, and of drawing to himself portions of the larger 

 bodies to which the microscopic organisms may be attached. For 

 these purposes nothing is so convenient as the Pond-Stick (sold by 

 Mr. Baker) which is made in two lengths, one of them sliding 

 within the other, so as when closed to serve as a walking-stick. 

 Into the extremity of this may be fitted, by means of a screw 

 socket, (1) a cutting-hook or curved knife, for bringing up portions 

 of larger Plants in order to obtain the minute forms of Vegetable 

 or Animal life that may be parasitic upon them ; (2) a broad collar, 

 with a screw in its interior, into which is fitted one of the sci*ew- 

 topped Bottles made by the York Glass Company ; (3) a ring or 

 hoop for a muslin Ring- Net. When the Bottle is used for collect- 

 ing at the surface, it should be moved sideways with its mouth 

 partly below the water ; but if it be desired to bring up a sample 

 of the liquid from below, or to draw into the bottle any bodies 

 that may be loosely attached to the submerged plants, the bottle is 

 to be plunged into the water with its mouth downwards, carried 

 into the situation in which it is desired that it should be filled, 

 and then suddenly turned with its mouth upwards. By unscrew- 

 ing the bottle from the collar and screwing on its cover, the con- 

 tents may be securely preserved. The Net should be a bag of fine 

 muslin, which may be simply sewn to a ring of stout wire. But it is 

 desirable for many purposes that the muslin should be made remov- 

 able ; and this may be provided for (as suggested in the "Micro- 

 graphic Dictionary," Introduction, p. xxiv.) by the substitution of 

 a wooden hoop grooved on its outside, for the wire ring ; the muslin 

 being strained upon it by a ring of vulcanized India-rubber, 

 which lies in the groove, and which may be readily slipped off and 

 on, so as to allow a fresh piece of muslin to be put in the place of 

 that which has been last used. The collector should also be fur- 

 nished with a number of Bottles, into which he may transfer the 

 samples thus obtained ; and none are so convenient as the screw- 

 topped bottles made in all sizes by the York Glass Company. It 



