LIMULUS AN ARACHNID, Hil 
tion of their surface of attachment, they have become more 
and more deflected into the cavity of invagination, moving 
on their fixed base at first backwards, then upwards, and 
finally forwards. As we now find them (in a spirit speci- 
men !), on viewing the inner surface of the ventral sclerites 
by removing the terga and viscera, they can be rotated on 
their hinge line so that they may be made to lie prone for- 
wards, exposing the stigma or opening of the pulmonary 
recess posteriorly, asin Pl. XXVIII, fig. 1 a, or they may be 
made to lie prone in the reverse direction, hiding from view 
the stigma, as shown in Pl. XXVIII, fig. 2 a, and in the 
woodcuts, figs. 6 and 7. The position which corresponds 
with that of the external appendages the pectines and the 
branchial organs of Limulus, when viewed from the posterior 
face, so as to show (in the case of Limulus) the lamelle, is 
that in which the lung-book is directed backward so as to 
hide the stigmatic aperture and is looked at from within the 
Scorpion’s body, that is, by dissecting off the terga, viscera, 
and muscles. ; 
When the pectines, lung-books, and branchial books are 
~ thas placed we find that the lamellz are not set precisely at 
right anvles vpon the axes, but obliquely, so that there is 
an imb ation of the successive lamelle. In all three it is 
the p oxi! lameila which is uppermost (see Pl. XVIII, fig. 
Zand x / and ig. 107’). The imbrication is identical in all. 
As to nui)cr of lamelle, we find in the pecten of Buthus 
Kochi eighteen (in other scorpions there are more or less) ; 
in the lung-books of some scorpions! as many as 130, and in 
the Limulus gill-book as many as 150. These numbers 
vary slightly, increasing with growth in al! probability. 
As to structure of lamelle, those of the pecten are more 
solid and strongly chitinised than those of the other two 
organs, but are, nevertheless, true ‘lamelle flattened 
transversely. 
Those of the lung-books are exceedingly delicate plates 
composed of two closely approximated membranes, between 
which the blood circulates ; they are, in fact, flattened bags. 
They carry on their free margins a few chitinous spinules 
(Pl. XXVIII, fig. 8). The lamelle of the gill-books of 
Limulus are similarly delicate flattened bags with a setose 
free border. I am not able to institute any comparison 
of the histological structure of the lamelle of the Scorpion’s 
lung-book with that of the King Crab’s gill-book, for 
although I have been able to work out that of the latter on 
: ' I believe the form in which I counted these to be a species of Androc- 
onus, 
