APPENDIX B. 



OSTRACODA. 



Places where to be found. They are to be found in lakes, 

 tarns, ponds, lagoons, canals, ditches, and often in very small 

 patches of water, and in slow-running streams' ; but in the latter 

 by no means commonly, except in weedy recesses protected 

 from the currents, or where clumps of thickly growing plants 

 abound. 



" Nowhere, throughout Scotland, is there any want of such 

 places either in number or variety, whether we regard the depth 

 of the water, varying from the thinnest covering to the deepest 

 lakes ; or their situations, ranging from the sea-level to high 

 mountain tarns ; or the character of the basin in which they lie, 

 rock, peat, clay, etc. ; or, lastly, the impregnated mineral con- 

 tents. Ostracoda are generally more abundant in the smaller 

 tarns or ponds, overgrown with weeds, than in deep and large 

 sheets of water, where the surging of the waves is unfavourable 

 to marginal vegetation ; yet I often find that places greatly 

 overgrown with plants are not always the richest in ostracoda, 

 but sometimes the reverse, probably in such cases by affording 

 more suitable conditions to a greater host of enemies. Ostra- 

 coda are occasionally obtained in small tarns and ponds where 

 the water has been nearly dried up, leaving only a little at some 

 central depression ; and even in the deep mud, where the water 

 has disappeared, good gatherings are met with, as well as in the 

 scanty water of furrows in old pasture land, and which are dry 

 during the greater part of the summer. It is indeed surprising, 

 as regards many of these patches of water, how speedily after 

 rain they are found swarming with ostracoda and other 

 microzoa. In some instances it has been observed that, after 

 the rains, certain species are absent which had been present 



