430 Birge — Vertical Distribution of Pelagic Crustacea. 



as it falls, pulls back the cover and opens the dredge. The 

 dredge is then raised through the desired distance — in our ex- 

 periments, 3 meters — and the larger or closing messenger is sent 

 down. This releases the closing weight, which pulls the cover 

 shut, and in so doing raises the opening weight. The dredge 

 is then drawn to the surface. It has been found that there is 

 no leakage of Crustacea into the dredge during raising. The 

 thin brass of the cover is tightly pressed against the frame as 

 soon as the upward movement begins, and the guides at the 

 edge of the cover present so narrow and tortuous a passage 

 that the water does not readily flow through it. Besides, the 

 guides are so constructed that the water displaced by the dredge 

 flows away from the groove and not into it. An examination 

 of the cut (PI. VIII, fig. 1) shows that the arrangement is such 

 that the animals are not likely to come in. In our numerous 

 hauls it was found entirely tight, so far as Crustacea were con- 

 cerned. Many times the dredge was hauled from the bottom of 

 the lake through water whose upper levels contained thousands 

 of Crustacea, and on opening was found to contain perhaps 6 

 or even fewer Crustacea, with, perhaps a Chironomus or Corethra 

 larva. Experimental hauls, sending down and raising the 

 dredge when closed yielded uniformly negative results. 



When the messengers arrive at the surface they are detached, 

 the dredge hauled up, and the contents washed down into the 

 bucket. This is removed and the catch washed into a collecting 

 tube, modeled on those designed by Prof. J. E. Eeighard of the 

 University of Michigan, made and used as follows: 



The bottom is cut from an eight drachm short homeopathic 

 vial, a piece of fine cloth is tied tightly over the neck, and a 

 cork fitted to the bottom. A rubber band is placed upon the 

 conical tube of the bucket, so that the collecting tube can be 

 pushed tightly upon it. The rubber cork is lifted from its 

 place in the bucket, the catch runs out into the collecting tube, 

 and the bucket is carefully washed down into the tube. The 

 water drains off through the cloth, the tube is detached, filled 

 from a large jar of alcohol, and placed in the jar, where it floats 

 cork uppermost, and requires no more attention until a con- 

 venient time offers. Most of our collecting was done at one 



