42 Moll. 
MOLLUSCA. 
for the growing shell. The anus is formed by rupture, not invagination ; 
the whole fore-gut is ectodermal, the mid- and hind-gut and stomach are 
endodennal in origin. The auditory sacs are formed about the tenth day, 
and sink inwards to the pedal ganglia. The heart arises in the form of 
a number of cells surrounding the rectum. The byssus-gland of the 
Glochidium is a special larval organ—an adaptive modification to its 
peculiar mode of life. 
For a sketch of the life-history of the Oyster, see Ryder (317). 
11. Stray Biological Notes. 
Oysters in the Firth of Forth lie on the flat valve ; Cunningham, 
Nature, xxxii. p. 597. The position varies according to the nature of the 
bottom, the flat valve being lower on rock, the convex on sand; Wort- 
ley-Stuart, t. c. p. 625. 
Left valve of the oyster fry always becomes attached. When they fix 
themselves to dead shells which have been thrown into the water for that 
purpose they become attached to the under surface, being thus protected 
from sediment. Ryder, op. cit. xxxiii. p. 81. 
Mobius [t. c. p. 52, and J. R. Micr. Soc. (2) vi. p. 52] states that, out of 
143 specimens examined, 43 which bore portions of the bottom had all 
rested on the left side. 
Segmentina lineata, Walker, spins threads ; Cockerell, Zool. (3) ix. 
p. 267. 
Aplysia lives at 26° C. (?), Pleurobranchcea dies speedily at 40°, Murex 
withstands for a long time a temperature of 30°, and Pecten for a shorter 
period ; Frenzel, Arch. ges. Pliys. xxxvi. p. 463. 
Variation of Littorina , see Haacke (152) and p. 86, posted. 
Cause of variation in Limncea sought in alternations of dryness and 
moisture ; Dodd, J. of Conch iv. p. 304. 
Remarks on adaptability to resist action of waves ; Hunt, Nature, 
xxxii. p. 243. 
The artificial culture of snails proposed by Ninni, # Rapporto a S. E. il 
Ministro di Agricoltura, &c. Rome : 16 pp. and map. 
Rissoa octona , Linn., prefers dark-blue and dark-green light to bright 
red ; Graber, SB. Ak. Wien, xci. 1, pp. 144-148. 
Some Tectibranchiata are carnivorous ( Scaphander, Phlllne , Dorldium ), 
some omnivorous ( Gastropteron, Pleurobmnchus), and others herbivorous 
( Aplysia , Notarchus ) ; Vayssiere (364). 
Snails eating whitening; Poulton, Nature, xxxiii. p. 176. 
A snail ( Helix aspersa) twice found its way to a special place, and was 
watched during the process ; Furtado, # Zool. Sect. Lisb. Mus. Act. 27, 
1885 [transl., Ann. N. H. (5) xvi. pp. 519 & 520]. 
Limpets return to same spot after feeding, but can also live long with¬ 
out moving ; prefer hard smooth surfaces to soft ones : probably do not 
bore rock : Robertson (311) ; see also Davis (103). 
Rate of growth of clams (Mya cirenaria) ; Ryder, Bull. U. S. Fish 
Comm. v. pp. 174-176. 
Helix pomatia lives 4-5 years in captivity ; Kinkelin (208). 
