386 NOTES AND COMMENTS [december 



Asterionella. 



The organism to which this elegant name pertains is a diatom recently 

 investigated by Messrs. G-. C. Whipple and D. D. Jackson {Journal of 

 the New England Water Works Association, vol. xiv. No. 1). It 

 causes trouble in water-supplies by producing objectionable tastes and 

 odours. It is common in Massachusetts waters, and its recent occur- 

 rence in the Brooklyn supply led to the investigations here recorded. 



The shape of this diatom resembles that of a humerus, and several 

 cells unite to form star-like clusters. The only species is A. formosa 

 (Hassall), but many varieties have been observed. The article itself 

 must be consulted for details of structure. 



The authors suppose that they saw spores or spore-like bodies in 

 the cells, but they did not observe any of these spores (?) developing. 



The diatom is widely scattered over Europe and North America, 

 and is found in large ponds, lakes, and reservoirs, where comparatively 

 clear water is stored. 



It is said to be more abundant near the surface than in the 

 depths. Normally it occurs in the spring and autumn, that is, 

 regularly after periods of stagnation ; but it is in ground waters stored 

 in open reservoirs that it attains its greatest development. By ground 

 water is meant water which has percolated through the ground. 



The numbers of Asterionella vary from 1000 to 6000 per cubic 

 centimetre of water. The odour at first is aromatic, then it resembles 

 that of geraniums, and finally it becomes very fishy. The smell 

 varies with the number of organisms in the water, and is due to a 

 substance analogous to the essential oils. 



A chemical analysis was made, and the mineral matter found to 

 be 57 per cent of the dry weight of the organism, and of this nearly 

 5 per cent is silica, which is present to a greater extent in ground than 

 in surface waters, hence the greater prevalence of Asterionella in the 

 former. 



The only practical suggestion possible is that reservoirs may be so 

 designed as to be easily isolated and cleaned whenever necessary. 



New Mice from St. Kilda. 



Me. Bakkett Hamilton has recently described [Proc. Zool. Soc. 1899] 

 two new species of mice from St. Kilda, and his paper is of interest 

 in its bearing on the role of isolation as a factor in evolution. At 

 the same time, since mice are very common animals whose variation- 

 statistics could be readily procured, one cannot at this time of day 

 accept these two alleged new British species as securely based unless 

 they are very thoroughly compared with the variations of Mus sylvaticus 

 and Mus musculus. Let us illustrate our difficulties. 



