180 THE MICROSCOPE AND ITS REVELATIONS. 



former may be designated as horizontal, the latter as vertical. Nothing 

 need here be added to the full directions for making such Sections, 

 which have already been given ( 192-194). Many of them are beau- 

 tiful and interesting objects for the Polariscope. Much valuable infor- 

 mation may also be derived from the examination of the surfaces 

 presented by fracture. The membranous residua left after the decalcifi- 

 cation of the shell by dilute acid, may be mounted in weak spirit or in 

 Goadby's solution. 



575. The animals composing the class of Cephalopoda (cuttle-fish and 

 nautilus tribe) are for the most part unpossessed of shells; and the struc- 

 ture of the few that we meet-with in the genera Nautilus, Argonauta 

 (' paper-nautilus'), and Spirula, does not present any peculiarities that 

 need here detain us. The rudimentary shell or sepiostaire of the com- 

 mon Cuttle-fish, however, which is frequently spoken-of as the ' cuttle- 

 fish bone,' exhibits a very beautiful and remarkable structure, such as 

 causes sections of it to be very interesting Microscopic objects. The 

 outer shelly portion of this body consists of horny layers, alternating 

 with calcified layers, in which last may be seen a hexagonal arrangement 

 somewhat corresponding with that in Fig. 390. The soft friable sub- 

 stance that occupies the hollow of this boat-shaped shell, is formed of a 

 number of delicate calcareous plates, running across it from one side to 

 the other in parallel directions, but separated by intervals several times 

 wider than the thickness of the plates; and these intervals are in great 

 part filled-up by what appear to be fibres or slender pillars, passing 

 from one plate or floor to another. A more careful examination shows, 

 however, that instead of a large number of detached pillars, there ex- 

 ists a comparatively small number of very thin sinuous laminae, which pass 

 from one surface to the other, winding and doubling upon themselves, 

 so that each lamina occupies a considerable space. Their precise ar- 

 rangement is best seen by examining the parallel plates, after the sinuous 

 laminae have been detached from them; the lines of junction being dis- 

 tinctly indicated upon these. By this arrangement each layer -is most 

 effectually supported by those with which it is connected above and 

 below; and the sinuosity of the thin intervening laminae, answering ex- 

 actly the same purpose as the ' corrugation ' given to iron plates for the 

 sake of diminishing their flexibility, adds greatly to the strength of this 

 curious texture; which is at the same time lightened by the large amount 

 of open space between the parallel plates, that intervenes among the 

 sinuosities of the laminae. The best method for examining this struc- 

 ture ; is to make sections of it with a sharp knife in various directions, 

 taking care that the sections are no thicker than is requisite for holding- 

 together; and these may be mounted on a Black Ground as opaque ob- 

 jects, or in Canada balsam as transparent objects, under which last 

 aspect they furnish very beautiful objects for the Polariscope. 



576. Palate of Gasteropod Mollusks. The organ which is sometimes 

 referred to under this designation, and sometimes as the ' tongue,' is one 

 of a very singular nature; and cannot be likened to either the tongue or 

 the palate of higher animals. For it is a tube that passes backward and 

 downwards beneath the mouth, closed at its hinder end, whilst in front 

 it opens obliquely upon the floor of the mouth, being (as it were) slit-up 

 and spread-out so as to form a nearly flat surface. On the interior of 

 the tube, as well as on the flat expansion of it, we find numerous trans- 

 verse rows of minute teeth, which are set upon flattened plates; each 

 principal tooth sometimes having a basal plate of its own, whilst in 



