NOTES AND MEMORANDA, 165 
so profound and deadly an influence on the nervo-muscular 
tissues of the Medusz, I was led to try some further experi- 
ments to ascertain whether it is, as Agassiz affirms, to the mere 
difference in density between the fresh and the sea water, or to 
the absence of the particular mineral substances in question, 
that the deleterious influence of fresh water is to be ascribed. 
Although my experiments led to no very instructive conclusion, 
they are, I think, worth stating. 
I first tried dissolving chloride of sodium in fresh water till 
the latter was of the same density as sea water. Sarsie dropped 
into such a solution continued to live for a great number of 
hours ; but they were conspicuously enfeebled, keeping for the 
most part at the bottom of the vessel, and having the vigour of 
their swimming-motions greatly impaired. The tentacles and 
polypite were strongly retracted, as in the case of exposure to 
fresh water, and the tissues also became slightly opalescent. 
Thinking that perhaps a fairer test would be only to add as 
much chloride of sodium to the fresh water as occurs in sea 
water, I did so; but the result was much the same. On now 
adding sulphate of magnesium, however, to the amount normally 
present in sea water, the Sarsie became more active. I next 
tried the effects of chloride of sodium dissolved in fresh water 
to the point of saturation, or nearly so. The Sarsze, of course, 
floated to the surface, and they immediately began to show 
symptoms of torpidity. The latter became rapidly more and 
more pronounced, till spontaneity was qnite suspended. 
The animals, however, were not dead, nor did they die for many 
hours—their irritability continuing unimpaired, although their 
spontaneity had so completely ceased. The tentacles and polypite 
were exceedingly relaxed, which is an interesting fact, as being 
the converse of that which occurs in water containing too small 
a proportion of salt. Lastly, to give the density hypothesis a 
still more complete trial, I dissolved various neutral salts and 
other substances, such as sugar, &c., in fresh water till it was of 
the density of sea-water; but in all cases, on immersing Sarsia 
in such solutions, death was as rapid as that which followed their 
immersion in fresh water.” 
Terminology of Reproductive Organs and Classification of 
Thallophytes.—Our readers are requested to substitute the fol- 
lowing table for the one given on pp. 419, 420 of the last 
number of the “ Journal.” 
We take this opportunity of thanking many correspondents 
for their kind and encouraging criticisms; and of making the 
following corrections and emendations. 
