372 The Naturalist of Cumbrae. 



before the ponds dried up, while by next season they again 

 become abundant. Whatever means of distribution there may 

 be, it is very probable that this renewed life proceeds in a great 

 measure from ova. That the ova retain vitality for a long time 

 is certain. The late Dr. Baird, of the British Museum, showed 

 Dr. G. S. Brady and myself a jar containing numerous forms of 

 animal life which had made their appearance from mud taken 

 from a dried-up canal in India during the hot season, and kept 

 in the dry state for a considerable time after reaching this 

 country before being subjected to water. Shortly after water 

 was supplied, many living forms made their appearance. 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 and 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 these 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. Ostracoda 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. These little bivalve crustaceans 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 Govan colliery dam, which is close to the terminus 



