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POPULAR SCIENCE REVIEW. 
the shell, to which it is attached by the margin of its mantle, to 
move forward in its habitation, and that its hinge-ligament and 
shell-muscles a,re absorbed behind, and added to in front, to 
accommodate themselves to the onward growth of the shell-border ; 
of necessity, therefore, the animal cannot let go its muscular or 
its siphuncular point of attachment to the old septal surface 
until the new one is made ready : hence the dipping down from 
layer to layer of the oyster’s shell-muscle (fig. 12); hence also 
the curious funnel-like tubes in Aturia * (fig. 4). 
Although, as we are quite ready to admit, no analogy can 
perhaps be drawn between these two forms, occupying, as they 
do, the one the highest and the other the lowest place in the 
Testaceous scale, yet there nevertheless seems to be a definite 
mode of growth in all shell-structures, which even the highly- 
developed Cephalopoda share with the rest. 
EXPLANATION OF PLATE LXXXII. 
Camerated Shells. 
Fig 1. Section of the shell of the Pearly Nautilus, Nautilus pompilius. 
Showing water-chambers (?) body-chamber, and siphuncle (Tetra- 
branchiata). 
„ 2. Spirula Icevis, New Zealand. 
„ 8. Aturia zic-zac. London clay, Highgate. 
„ 4. Broken shell of Aturia zic-zac. Miocene, Dax, to show funnel- 
shaped siphons. 
„ 5. Section of Euomphalus , showing septa. Carboniferous limestone, 
Bolland, Yorkshire. 
„ 6. Section of Triton corrugatus, showing septa formed in apex of spire. 
„ 7. Magilus antiquus, Bed Sea. The magilus lives fixed amongst corals, 
and grows upwards with the growth of the zoophytes in which 
it becomes immersed ; it fills the cavity of its tube with solid 
shell as it advances. 
„ 8. Vermetus lumbricalis (young), West Africa. 
„ 9. Part of an old tube of Vermetus maximus , showing septa. 
„ 10. Part of tube of Teredo antenautee , London clay (cut to show septa). 
Wetherell collection. Sheppey. 
„ 11. Shell of Caprinella triangularis , Dem. (one of the Hippuritidce). 
U. Greensand, Bochelle. 
,, 12. Section of an aged oyster ( Ostrea Boblayei), showing indentation in 
each shell-layer where the muscular attachment was fixed. 
* The same structure is noticeable in the delicate little nacreous and in- 
ternal shell of spirula (fig. 2). 
