60 . 
Shells. 
S.A. 
NAl*., VOL. 
Februarv, 
XIV. 
1933 . 
chambered Nautilus shell which has gradually been pushed back 
in the course of its spiral and only the flattened aperture and the 
earlier chamber partitions closely packed, like a pack of cards,, 
remains (fig. 6A, C,) 
Indeed at the rear end of the Cuttlebone may still be seen 
a degenerate rostrum, so large and heavy in the fossil specicsj 
but here reduced to an insignificant useless spine which Is lost 
in tlic adults of some Cuttlebones, but always present in the 
Cuttlebone. E.j D . — Supposed intermediate stages. 
juveniles. The Octopus is another example of the Cephalopoda. 
but here the shell is entirely lost, though a small cartilage In the 
back indicates its former presence. Although without internal 
shell or skeleton on which to obtain leverage, the octopus is ex- 
ceedingly strong. The suckers, even in a dying specimen, need 
all one’s strength to detach them from their hold. 
The Cephalopoda and the next kind of Molhisca, the Gastro- 
poda, are provided with a ribbon-Iikc tongue beset with teeth, 
and used for grinding food. As the teeth are worn the ribbon 
moves forward, bringing new teeth into position. The Gastro- 
poda are distinguished by their spiral shell, which is really a 
gradually widening tube wrapped spirally on itself. This usu- 
ally turns to the right, but rare, abnormal specimens turn to the 
left. When this occurs, the various organs in the animal arc 
also transposed as in the rare case of a transposition in a human 
being, where the heart, appendix, spleen, and other organs are 
on the right side and the person is consequently truly left-handed. 
However there is another form of abnormality, the ultra-dextra! 
shell where the spire has been, as it were, pushed through the 
