128 
REPORT— 1847, 
thin slices, and being perforated by an immense number of minute sloooiii 
tubuli, which run nearly parallel to one another from one surface of the sbfl 
to the other. This arrangement may be seen by making a thin section of 
any part of the shell; but it may be shown particularly well in the end oflbt 
claw, which is thicker and of denser texture than the rest. A transnnt 
section of this shows the tubes radiating from the central cavity towud<L» 
external surface, and would, 1 fool assured, be regarded by the mostujf' 
rienced observer as the section of a tooth, if he were not informed of iur.:! 
nature.” 
124. Of the horny epidermic membrane it is not requisite to say anjdiiitf 
additional. It is easily detached I'roin the subjacent layers, after the shell b 
been immersed for a time in dilute acid ; and I find M. Lavalle in accordaw 
with me in the statement tliat it presents no trace of struciurn. Tlicpigmeolr] 
layer, which it covers-in,presculs(when exaruined with a sufficiently bigbniM- 
nitying power) the clearest possible indications of cellular arrangcnicntlif- 
79) ; and I can therefore only attribute to the want of a sufficiently tniautfO- 
amination ol his object the veryiiuperfeet account of the structure of thahji^ 
pven by M. Lavalle. “ Examined by its surface," he says, “the pigmrDOtl 
layer often presents a well-marked areolar asjiect The Luptta dicantk^^ 
sents a good example of this organization. liere,as in the majority of 
the polygons which by their junction form this surface, are nearly regulaf- 
and most commonly present six sides. In some cases there may be remarkw 
in the middle ot nearly all these polygons a little prolongation which appfW' 
to belong to the epidermic layer. Is this appearance due to veritabV 
lines disposed in a regular network? Or is it mtlier produced byUttle/i=®»- 
TrnlliE pressed against each otlier, of which we can only distioguisb the/of 
iws ol separation ? 1 am of this last opinion.” Tlie representation giT« 
c ^70 L? . . *1*® P>ff'»>e«tary layer oi Lvptsa rAcowtA^ closely 
Iig- 78, which IS a view of the pigmentary layer in the common Crab 
paffurus) under a low magnifying power. Hut when a sufficiently thin ^ 
tion IS examined by transmitted light with a high magnifriug power, dr 
character of the network, ami of the dark spaces which it encloses brew®' 
at once apparent («g. 79). It U then obvious that the nearly 
polygonal reticulations are the thickened 7 calls of cells, each of 
seen to be divided by a distinct line, xvl.ich marks tl.c junction ofthecoc^ 
Ti“^ * colouring matter or with some other semi-opake 
tS eSlnJif is not confined to the coloured parts of the 
and W, on the white undcr-surraceolffiebo^ 
Su colouring layer seems 
<^311 be detacliedfrom tbelaj- 
tWk p^ placed in dUute acid. 
lobster* to be thus separately 
kZ m?m tins point; but I should be disposed t? think tlmt 
remarkab e thickness. l*he prc*scnce of the niffmentarv laver has bcea if- 
libTtnd ® numlmrof Decapod Crastaceaof^. 
ne^ ^ ‘ >n»tancea it is of very consiilerable ^ 
In the^rl^ tt t* the thickest of the tliree levers of the 
it presents, accordingto 
in a d r^n r ^rncture, a variable number of extremely fine 
out an« and to each other, 
hut the^v\oL*aamher is usually from six ^ 
y sometimes considerably exceed the larger of these amounts, be‘>B 
