274 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
stoma nigrum in specimens occurring in two lakes in Indiana. He finds 
that tLe specimens of both species found in one lake differ from those 
found in the other lake, that the variations are determinate for each 
lake, and that the successive broods vary with the varying conditions 
of the year in which they are born. In Etlieostoma caprcdes the males 
are more variable than the females ; in E. nigrum the females are more 
variable than the males. There is a correlation between the variations 
of the two fins ; thus, when the dorsal spines increase in number, the 
dorsal rays decrease ; when the anal rays increase, the dorsal spines 
and rays and the sum of the elements in the two dorsals increase. 
Variation versus Heredity.* — Mr. H. S. Williams, without having 
sufficiently thought out the terms which he uses, argues in support of 
the proposition that “ variation, and not heredity, is the fundamental 
characteristic of the phenomena of organisms.” But heredity is only 
a term for the relation between successive generations. 
Mr. Williams also maintains, in support of his thesis, that the actual 
result of selection is the retarding and checking of variation ; that vari- 
ation is but a phase of the fundamental genetic process peculiar to living 
organisms ; that every act of variation is anterior to experience, and 
thus is necessarily original and genetic, whereas every hereditary act is 
necessarily secondary to, and the result of experience ; and so on. 
INVERTEBRATA. 
Mollusca. 
Fresh-water Molluscs of Celebes.f — Herren P. and F. Sarasin give 
an account of these, and one of their most striking results is to show 
that the central lakes contain an ancient and isolated fauna. Thus the 
Posso lake, which harbours two genera peculiar to itself — Miratesta and 
Tylomelania — has not a single foim in common with the Matanna and 
Towuti lakes connected with it by a river. 
y. Gastropoda. 
Nervous System of Gasteropods.if — Professor Henri de Lacaze- 
Duthiers has an important paper on the ganglia called pallial and 
stomato-ga9tric in certain Gasteropods. Additional researches on the 
subject have deepened his conviction that it is better to consider the 
central nervous system as a whole, rather than to attempt to ascribe 
special functions to its parts. Further, he is of opinion that when any 
organ in a Gasteropod becomes much specialised, it is chiefly the peri- 
pheral part of the corresponding portion of the nervous system which 
becomes modified, while the true centre for the organ alters little or not 
at all. The development of accessory ganglia on the peripheral nerves 
often, however, greatly obscures the homologies. As to the nomen- 
clature of that part of the central nervous system which lies beneath 
the gullet, he prefers to call the whole mass of ganglia the unsym- 
* Amer. Nat., xxxii. (3898) pp. 821-32. 
t ‘Die Siisswasser-Mollusken von Celebes,’ Wiesbaden, 4to, 1898, 104 pp. and 
13 pis. See Zool. Centralbl., vi. (1899) pp. 200-3. 
X Arch. Zool. Exper., vi. (1898) pp. 331-428 (4 pis. and 10 figs.). 
