THE president's ADDRESS. 35 



there is a good account in the " Intellectual Observer," Vol. 2^ 

 by the eminent writer above named. By which it appears, that 

 this terrible disease attacks the bones of the lower extremities^ 

 and the victim dies of exhaustion. The fungoid species in 

 question has been placed with the Mucors or Moulds, and, in 

 the article referred to, is an illustration of it by the late Dr. 

 H. J. Carter, E.R.S. ; and I was particularly struck by the close 

 resemblance it has in character with an illustration of mine in 

 one of the objects from the Varne Sand, to which I gave the 

 provisional name of Saprolegnia Varniensis. The analogy is^ 

 remarkable as seen in the mvcelia, as also in what appears to 

 be the development of sporangia {vide PL XV., Figs. 3, 4, Vol. 1, 

 Ser. II., of our Journal.) It agrees with my argument on the 

 nature of evolution, arising from differences of conditions; and 

 the large family of Mucors may be set down as potent destroyers 

 closely allied to each other. 



I have alluded to what is constant and continuous in nature's^ 

 law, which may now bring us to consider changes to which we 

 must equally have our attention directed. Every naturahst must 

 at times take note of the disappearance of organisms where they 

 formerly abounded. The variations of the seasons, a succession 

 of droughts, or a succession of wet with storms, necessarily affect 

 the conditions of life. Then we have to take into account the 

 neighbourhood and increase of large towns, and physical changes 

 inevitable from drainage. The latter will especially affect the 

 hunting grounds of the microscopist, and it is felt at Hampstead 

 Heath and other suburban resorts. But I have often found 

 changes where there were no altered conditions, at least apparent^ 

 especially as regards the Diatomacese, and of course it would be 

 equally seen in other organisms of a like kind or lower type. 

 We do not know the law thus operating, but can easily 

 understand that physical conditions are answerable for most of 

 the changes observable. But if the extension of our towns is 

 inimical to some animal or vegetable natures, it may be favour- 

 able to others. It is not every plant that dislikes the excess of 

 carbon, and there may be some of the minute organisms on the 

 animal side equally agreeable to it. 



In the neighbourhood of London, indeed throughout its 

 geological basin, earth thrown up from an excavation is im- 

 mediately productive of the well-known plant the colt's-foot ; and 



