30 



within a dozen of yards or so, and is generally covered with a 

 sprinkling of soot from the neighbouring factories. It is further 

 the play pond for the children of the vicinity to sail their small 

 boats upon. In spite of all these apparent disadvantages against 

 the Ostracoda, I seldom fail to obtain a fair gathering of them in 

 this small patch of water, whether in summer or winter. Their 

 survival under all these circumstances may be that what is harm- 

 less and healthful to them may be death to their enemies. The 

 Gypridce proper are seldom if ever found in very deep water, but 

 mostly amongst the vegetation, while the Gandonce are met with 

 at greater depths. In Lochlomond I have found them at a depth 

 of 40 fathoms. Although these small crustaceans appear to be 

 greatly more abundant on the plains than on the mountains, Dr. 

 Gr. S. Brady records Gypris cinerea, G. compressa, G. striolata, &c., 

 from a pool near the summit of Mickle Fell in Yorkshire, at an 

 elevation of 2000 feet. 



From the foregoing it is evident that the abundance of these 

 organisms in one place cannot alwaj^s be taken as an index of their 

 profusion in another, although the two may be of quite similar 

 appearance. In the one, these forms of life may be swarming ; 

 in the other, absent or nearly so. So little can we depend upon 

 apparent similarity in this respect that, in collecting, it is well to 

 make trial of even the most unlikely spots, and, although we 

 may meet with frequent disappointments, we shall, on the other 

 hand, often find what we will deem prizes where they are least 

 expected. 



2, Time for Collecting. — The best time for collecting these 

 organisms is in summer, as they are then met with in the greatest 

 abundance. There can be little doubt that heat is conducive to 

 their increase and development. In a hot-house tank, where the 

 heat was kept up to about 65° Fahr., one species of Ostracoda 

 {Gy-pris incongruens) was abundant. In another tank outside of 

 the building, where the water was supplied from the same source, but 

 to which artificial heat was not imparted, the same species was 

 present, but comparatively few in numbers. How far an increase 

 of temperature may contribute to their increase of numbers or 

 improvement of condition, or how far it may be borne with impunity, 

 does not seem to be accurately known. Dr. G. S. Brady states 

 that he has found them in the water of mill cooling ponds at a 

 temperature of 100° Fahr., and the water might at times be even 



