32 



all that were seen remaining of a species so numerous on a 

 former occasion. It was, however, plentifully replaced by Cypris 

 virens, which, on the other hand, had been wholly absent in the 

 first gathering. 



On March 9, 1879, after the severe frost, the dam was again 

 visited. It showed little new growth of vegetation, further than some 

 straggling blades of grass, the sides still fringed with the old 

 autumnal weeds. There was no great variety found this time. 

 Cypris reptans was wholly absent, so was Cypris virens. The pre- 

 vailing Ostracod now was Cypris compressa. 



Another gathering was taken on May 21, 1879, just a year after 

 the first trial was made. On this occasion there were no confervas 

 nor Cypris reptans, both so abundant on the same date last year, 

 showing that we cannot be certain of finding even the same species 

 where they had been abundant in the same month of the previous 

 year. This probably depends on the time of reproduction, or to 

 some extent on the different varieties of animal and vegetable life 

 that abound at the various seasons, and are more or less favourable 

 in respect of food, shelter, etc., to the different species of Ostracoda. 



3. Mode of Collection. — Unlike the marine, the fresh and 

 brackish- water Ostracoda are within the reach of everyone, and 

 the mode of capture is so easy that it can offer no obstacle to the 

 pursuit. They are generally collected with a hand net; but when 

 it is desirable to examine the ooze from the bottom of deep lakes, 

 a boat and dredge are necessary. The size of the net usually 

 employed has the ring of the mouth about 10 inches in diameter, 

 and the net about 20 inches deep. Such nets are to be had ready- 

 made, which screw from the handle and fold into 3 segments, so as 

 to be more portable. In my own experience, I find one of much 

 smaller size very efficient, one without the folding joints, having 

 the ring only 6 inches in diameter, and the muslin bag not less 

 than 24 inches deep, and rounded at the bottom. The greater the 

 proportion the bag is to the ring the more freely the water will pass. 

 The mesh of the net may be about 100 threads to the inch. The 

 ring is made of ^-inch brass wire, which is strong enough to bear 

 the pressure amongst pond weeds, or in raking the mud from the 

 bottom. A socket or screw projects from the ring for the reception 

 of the handle, whether a walking-stick or other rod more or less 

 long. 



A rod from 6 to 9 feet long has a great advantage over a 



