S30 j\li'. R. Warington on Preserving the Balance bcttceen 



in theory first suggested themselves to my own mmcl, uamely 

 the Chlorosperms. After making mimerous unsuccesslul expe- 

 riments with both the brown and the red varieties of Algte, 

 I was fully convinced that, under ordinary circumstances, the 

 greeia weeds were the best adapted for the purpose. 



This point having been practically ascertained, and some good 

 pieces of the Enteromorpha and Ulva latissima in a healthy state, 

 attached to nodules of flint or chalk, having been procured 

 fi'om the shore near Broadstairs, several living animal subjects 

 were introduced together with the periwinkle. Everything pro- 

 gressed satisfactorily, and these all continued in a healthy and 

 lively condition. 



My first trials were conducted in one of the small tanks which 

 had been used for fresh water ; but as it was necessary, dui'ingthe 

 unsuccessful experiments with the brown and red sea-weeds, to 

 agitate and aerate the water, which had been rendered foul from 

 the quantity of mucus or gelatinous matter generated during the 

 decay of their fronds, until the whole had become oxidized, and 

 the water rendered clear and fitted for another experiment, it 

 was, therefore, for greater convenience, removed into a shallow 

 earthen pan and covered with a large glass shade to protect the 

 surface of the water, as much as possible, from the dust and soot 

 of the London atmosphere, and at the same time impede the 

 evaporation. In this vessel then I had succeeded perfectly in 

 keeping a large number of beautiful living specimens in a healthy 

 condition up to the close of 1852. I therefore gave instructions 

 for the making of a small tank as a more permanent reservoir, 

 and one more adapted for carrying on my observations and 

 investigations on the oeconomy and habits of the inhabitants. 



From the experience I had obtained in my experiments with 

 the freshwater tank, I was induced to modify slightly the con- 

 struction of this vessel ; thus, at the back, or part towards the 

 light, the framing was filled with slate in the same way as the 

 ends and bottom ; for I had found that the glass, originally em- 

 ployed, very soon became covered with a confervoid growth 

 which had an unpleasing appearance to the eye, and in conse- 

 quence of which I had been obliged to paint the glass on the 

 exterior to prevent this growth from increasing to too great an 

 extent. It was also an vrnnatural mode of illumination, as all the 

 light should pass through the surface of the water. The front 

 towards the room and the observer was constructed of plate- 

 glass, the whole being set in a stout framework of zinc, and 

 cemented with what is known under the name of Scott's cement, 

 and which I have found to answer for the purpose most admi- 

 rably. Within this tank were arranged several large pieces of 

 rock-work, thrown into an arched form, and other fragments 



