MONSTROSITIES 
107 
Figs. 229. 230, 231.— 2^. pengra (Mull.)xll, 
A pool, near Geneva, 
Collected by Dr. A. Brot, 
Showing the deformation of the columella 
and the base of shell, assumed to be caused 
by Hydra viridis. 
Dr. A. Brot has shown how some of the lowliest organisms may 
influence even the form of the shell 
in the mollusca, as he records that 
during one season nine-tenths of 
the specimens of Limncva peregra 
living in a pool near Geneva, were 
curiously malformed at the base of 
the columella and anterior part of 
the shell generally; this malforma- 
tion, which was correlated with a certain dwarfing of the shell, was 
concurrent with an extraordinary abun- ^ 
dance of Hydra viridis in the same pond. 
The following year the Hydra had dis- 
appeared, and this disappearance of the 
Hydra was coincident with the disappear- 
ance of the peculiarity in the shell, of 
which the Hydra was apparently the ^ rTeiela,''^ ^ 
. 1 -j. Collecied by Dr. A. Brot, 
plllUcliy CtlUSC, fliS tilG SnCCGGulll^ ^GllGlcl- Showing the normal form as found 
, • !• r • *x 1 the pool with the malformed in- 
tions of tlie Lunnoja were ij^uite normal, dividuais. 
Herr Julius Hazay has also observed and recorded that the 
“invasion” of the shell by the leech 
may greatly influence the character of 
the growth in Liiimau stagnalis, by 
causing the animal to gibbously inflate 
the outer margin of the aperture of 
its shell on attaining maturity. 
Dreissensia pulymorpha, like other 
attached shells, is liable to malforma- 
tion, owing to interferences during 
growth, conseiiuent upon their situa- 
tion in crevices and from contact with 
hard substances. This species also 
often causes distorted and irregular growth in Anodonta and other 
Fig. 'I'Si. — Liinna'a stagnalis (L.), 
Buda-Pesth, 
(after Herr J, Ha^ay), 
Showing the inflected lip, said to be 
owing to the “invasion” of a leech. 
their 
valves together 
with its 
freshwater bivalves, by fastening 
byssus. 
It has been stated by Prof. Alplueus Hyatt that distortions of 
Univalve freshwater shells have usually occurred in still, enclosed 
waters with no outlet, and, although this is generally, it is far from 
being universally true. 
