594 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
historical introduction and a discussion of the physiological effects of 
fresh water on organisms unaccustomed to it, he submits a great body 
of facts illustrating the varied power of survival exhibited by those 
animals whose medium is changed. It will give some idea of the 
detailed character of Don Gogorza’s investigations when we note that his 
observations extend to over seventy different species, from liydroids to 
fishes. 
The proportion of deaths increased with the percentage of fresh 
water added to the salt. A certain amount of dilution all the marine 
animals experimented with seemed able to endure, but in each case 
there is a limit beyond which death rapidly ensues. This limit varies 
with the individual species, but not in correspondence to zoological 
relationships. In the various mixtures the Crustaceans showed them- 
selves most sensitive to the presence of fresh water, the fishes least. 
In the great majority transference to fresh water is rapidly fatal. In 
average power of resistance the groups of animals stand thus : — 
Coelenterates least, then Echinoderms, Tunicates, Worms, Fishes, 
Crustaceans, and Molluscs. A great deal depends on the rate of 
endosmosis permitted by the skin and cuticle. 
After a discussion of the causes of death in fresh water — by hydra- 
tion of the tissues, turgescence of cells, coagulation of albuminoids, &c., 
the author discusses the power of gradual adaptation to fresh water, 
which, as is well known, is exhibited by not a few, especially littoral, 
marine animals. 
Central Nervous System of Lower Animals.* — Prof. G. Ketzius 
has, in his further investigations, made use of the methylen-blue method. 
In the study of Worms he finds that closely allied species behave 
differently to the stains, and for almost every species it is necessary 
to make some slight change in method so as to obtain the best results. 
Attention was chiefly given to Polychseta and Hirudinea. There 
is an important agreement in the typical form of the elements of the 
nervous system of Worms, and in this they agree with the Crustacea. 
In both groups the ganglion-cell is, with rare exceptions, unipolar, and 
it gives oil* its process directly or indirectly to the periphery, where, as 
a nerve-fibre, it passes to its terminal branchings. On their course 
through the ganglia the trunk-processes give off secondary processes in 
various directions. These fine secondary processes generally branch 
dichotomously and repeatedly, and give rise to the chief mass of the 
dotted substance. There is formed an extraordinarily intricate plexus, 
or “ neuropilem,” but no network of anastomosing processes. 
The composition and arrangement of the dotted substance is very 
different in various worms, and the elements themselves differ con- 
siderably. 
Amphioxus lanceolatus and Myxine glutinosa fall under the head of 
lower forms. In the former there are all kinds of ganglionic cells ; 
“ true ” and “ untrue ” unipolar cells ; by the latter are meant cells 
which give off a thick process which soon branches, hut the process is 
considered to be a part of the body of the cell. To this type belong 
* ‘ Biologische Untersuchungen,’ ii., Stockholm, 1891, large folio, 53 pp., 16 pis. 
See Biol. Centralbl., xii. (1892) pp. 413-6. 
