1 
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. J therefore gave instruc- 
tions for the making of a small tank as a more permanent reservoir, 
and one more adapted for carrying on my observations and investiga- 
tions on the ceconomy 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 construction 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 employed, very soon became 
covered with a confervoid growth which had an unpleasing appear- 
ance to the eye, and in consequence of which I had been obliged to 
paint the glass on the exterior to prevent this growth from increasing 
to too great anextent. It was also an unnatural 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 admirably. Within this 
tank were arranged several large pieces of rock-work, thrown into an 
arched form, and other fragments were cemented in places against the 
slate at the back and ends, and at parts along the water-line, so that 
the creatures could hide themselves at pleasure; a short beach of 
pebbles was also constructed in order that shallow water could be re- 
sorted to if desired. The whole tank was covered with a light glass 
shade to keep out the dust and retard evaporation. 
With the sea water obtained in January, 1852, I have been working 
without cessation up to the present time, agitating* and aérating when 
it became foul during the unsuccessful experiments on the sea-weeds, 
but since then it has been rarely ever disturbed ; the loss which takes 
place from evaporation being made up, as before stated, with rain or 
distilled water. 
For a considerable period, after commencing these experiments, 
I was much troubled to obtain living subjects in a healthy condition, 
but having alluded to this, and the success of my investigations, 
in a short notice appended to a paper published in the ‘ Annals’ for 
* It must be decidediy understood that no agitation or so-called aération is 
required when the balance of animal and vegetable life is properly established. 
