mVEKTEBRATAj CRYPTOGAMIA, MICROSCOPY, ETC. 789 



except in weedy recesses protected from the currents, or where clumps 

 of thickly growing plants abound. They are more abundant in the 

 smaller ponds overgrown with weeds than in deep and large sheets of 

 water. Even in damp mud, and in the scanty water of furrows in old 

 pasture land, good gatherings are met with. Where the pools are 

 small and subject to be dried up during summer, they seldom contain 

 many species, although in such cases one species may prevail greatly. 

 Limestone districts are favourable to Ostracoda, but all rock or clay 

 surfaces are better than peat. Where there is nothing but pure peat, 

 or peaty ponds fringed with Sphagnum, few or no Ostracoda may be 

 expected. They are seldom searched for successfully where the lakes 

 or pools have risen much by heavy rainfalls, nor in mill-dams, where 

 the water is drained off rapidly, leaving broad, bare margins. It is 

 otherwise where the water in the pools is decreasing gradually by 

 evaporation. Then the animals appear to have time to follow the 

 water, and may be taken abundantly when thus brought closer together 

 in the small shallow pools left here and there. Moorland roadside 

 ditches are more promising than those at some distance from the 

 road. This may arise from a supply of material from the drainage of 

 the road, which may be requisite to build up the shells of these 

 minute crustaceans. They are seldom absent in ditches or marshes 

 which contain a little ochreous deposit with a metallic bluish scum on 

 the surface of the water ; they are more common in broad shallow 

 ditches than in those more narrow and deep, and are rarely met with 

 in springs or in ponds abounding with fish. Neither do they thrive 

 where Amphipods prevail. They are not always fastidious in their 

 choice of habitat, sometimes disporting in pure fresh water, at other 

 times revelling in water of very questionable character ; while others 

 affect brackish water, although they live in very different degrees of 

 the saline element. 



The best time for collecting is of course the summer, during sun- 

 shine. Heat is conducive to theii" increase and development. In a hot- 

 house tank at 65^ F., Cypris incongruens abounded, but in water from 

 the same source at a lower temperature there were comparatively few. 

 Dr. G. S. Brady found them in mill cooling ponds at 100^ F. They 

 may be found, however, under the ice in winter. 



The preferabL- mode of collection is a net 6 inches (rather than 

 10 inches) in diameter and 24 inches deep — the mesh one hundred 

 threads to the inch. This smaller size of net has the great advantage 

 of admitting conveniently a brass wire sieve with a hoop about an 

 inch deep to fit into the ring of the muslin net, preventing weeds 

 and other coarse material from getting into the bag, but sufficiently 

 open to allow all the Microzoa to pass through. A sieve with a 

 ^-inch mesh is very suitable. Tins protecting sieve requires to bo lilted 

 together into the mouth of the muslin net, so as not to fall out when 

 working, but sufficiently easy to be taken off when the contents of the 

 bag are turned out. For security, it is better to have the sieve slung 

 to the neck of the handle by a short cord. 



To work the net, sinqily sweep it through the vegetation along 

 the margin of the pond ; this done, remove the sieve, invert the bag. 



