288 



growth and development of the young fish. The plankton of Turkey Lake is here 

 considered as an environment rather than as including a large portion of its 

 inhabitants. As yet very little has been done toward classifying the various 

 organisms composing it, but a great portion of it is .crustaceans. 



The net used in determining the quantity of plankton is essentially the same 

 as those used by Hensen, Apstein and Reighard. The upper part consists of a 

 truncated cone of canvas, supported by an iron framework. The diameter of the 

 upper or smaller end of this cone is 33.35 cm. and of the larger or lower end 49 cm. 

 The slant height is 36 cm. • 



The net proper is made of Dufour's No. 20 bolting cloth. It is a truncated 

 cone with a slant height of 8() cm. The larger end is attached to the iron ring 

 supporting the larger end of the canvas cone. To the smaller end is fastened a 

 flat metal ring which supports the bucket. Three ropes attach this flat metal ring 

 to the framework of the canvas cone. This relieves the net proper of the weight 

 of the bucket. A twine net of inch mesh surrounds the net, serving to protect it 

 and to remove as much strain from it as possible. 



The bucket is a metal cylinder 6.5 cm. in diameter and 7 cm. deep. A flat 

 metal ring is attached to the top. Through this pass three binding screws, which 

 fasten the bucket to the ring on the bottom of the net. The sides of the bucket, 

 except three narrow strips, are cut away, making three openings, 30x50 cm. 

 These openings are covered with a wire gauze which has 77 percent, of its surface 

 solid and 23 per cent, open for the passage of water. The No. 20 bolting cloth 

 has S3 per cent, of its surface solid and only 17 per cent, open for the passage of 

 water. But an examination of water sti-ained through each proved that the wire 

 gauze is as efiective a strainer as the cloth, and when water rich in plankton is 

 forced through each by means of a pipette the gauze is the more effective strainer 

 (Eigenmann, 1895). The bottom of the bucket is cup-shaped and has a small 

 opening in the center. This opening is closed by a rubber stopper through which 

 passes a short glass rod that enables one to remove the stopper conveniently. 

 Three legs, each 10 cm. long, support the Ijucket. 



Three ropes radiating from an iron ring are attached to the framework of the 

 canvas cone and support the entire net. The rope which is used in drawing the 

 net up is attached to this iron ring. This rope is measured off' into feet or frac- 

 tions of a meter, so the depth to which the net descends can be determined easily. 



The plankton boat is provided with a swinging derrick in the stern. In the 

 end of this derrick is a pulley through which the net rope passes. The derrick ia 

 high enough to allow the net to swing clear of the sides of the boat, so that the 

 net may be swung into the boat after a haul has been made. (Eigenmann, 1895.) 



