576 L. E. CRAWSHAY. 



peptone on the 1st day, and again in smaller quantities on 5 days succes- 

 sively, from the 8th to the 12th day. 



5 small Calanoids were observed alive on the 42nd day. 



In both of these last-mentioned experiments the water became ex- 

 tremely foul on the 3rd day especially. In the second it was siphoned of! 

 and back into the bell-jar on that day, for aeration. In the first, it was 

 not disturbed. 



In these extreme cases, in which the Bacteria were grown, sometimes 

 repeatedly, in enormous numbers, the specimens were directly exposed 

 to the chemical changes produced in the water, apart from the intervals 

 when it was cleared, for about 4 or 5 days or longer as often as the Bac- 

 teria growth was renewed. In No. 121, for example, at least 2 Calanoids 

 survived, after nearly 7 weeks, an aggregate period of intense Bacteria 

 growth amounting to about 16 days. And in most cases the water 

 was not aerated or disturbed. From those results and from others 

 obtained in similar experiments, it seems evident that the influence of 

 common Bacteria of this character, occurring in comparatively small 

 numbers in the ordinary experiments, must be so slight as to be almost 

 negligible ; while the occurrence of Infusoria in the water can only be 

 regarded as counteractive to them, and probably as beneficial in the 

 presence of any unhealthy conditions that arise. 



In all of these experiments no food was given other than was already 

 present in those in which the water was unsterilised. Apparently the 

 specimens were feeding on the Infusoria, and judging from the appear- 

 ance of the excreta this seemed to be the case. 



So far as they have been observed, the Bacteria which can be of 

 serious harm to Copepoda in such experiments seem to be of infrequent 

 occurrence in the water employed. Two forms only have been definitely 

 recorded, to both of which allusion has already been made : the one 

 forming irregular white slimy strands through the water (p. 566) ; 

 the other giving a carmine-coloured tinge to objects attacked or 

 invested (p. 565). Each of these has been twice observed, and both 

 have proved in each case quickly fatal to all specimens that were con- 

 tained in the infected vessel, though an endeavour to cultivate the 

 second form has twice failed. 



