528 PROFESSOR E, RAY LANKESTER. 
united across the middle line by a soft plate-like fold of the 
sternal integument ; the result being that a plate-like body is 
formed from two originally distinct right and left appendages. 
On the under surface of each of the combined appendages 
a series of very delicate lamelle is found corresponding to 
the lamelliform teeth of the Scorpion’s comb-like organs. 
Ninth, tenth, eleventh, and twelfth appendages.—In 
Limulus, corresponding to the tergal areas marked Ix, x, x1, 
XII, we find a series of pairs of appendages precisely similar 
to that belonging to the eighth segment. 
In Scorpio it will be remembered that in the embryo 
rudimentary appendages appear corresponding to the first 
six abdominal segments, or the seventh, eighth, ninth, tenth, 
eleventh, and twelfth of the whole body. Of these the first 
pair we have seen, become in all probability the genital oper- 
culum ; the second pair are known to become the ‘‘ pectines ;”” 
the pairs on the ninth, tenth, eleventh, and twelfth segments 
disappear, as the lung sacs on those segments develop by a 
process of invagination. 
They disappear, but only from view. It has not been 
shown by actual observation, but it cannot well be doubted, 
that these rudimentary appendages sink within the lung- 
invaginations, and become the lamelligerous appendages 
which are found in them in the adult Scorpion. 
The four pairs of stigmata on the ventral surface of the 
ninth, tenth, eleventh, and twelfth segments of the Scor- 
pion’s body (woodcut, fig. 8) lead into sacs, each of whch con- 
tains, concealed within it, an appendage consisting of an axis 
bearing a series of delicate lamellae (woodcuts, figs. 6 and 
eX S, Royce, Tete). 
Each of these concealed appendages is strictly comparable 
in structure to one of the comb-like organs of the eighth 
segment, the axis corresponding to the axis, and the delicate 
lamellz to the teeth of the comb. 
Thus, then, we find five pairs of lamelligerous appendages 
on the five segments of the Scorpion’s body numbered 8, 9, 
10, 11, 12, of which the first pair is external, and accordingly 
modified, whilst the next four are sunk below the surface, 
and accordingly modified. In Limulus, on the exactly cor- 
responding segments, namely, those numbered 8, 9, 10, 11, 
12, we find five pairs of lamelligerous appendages, but these 
are all external, and all alike modified for the purposes of 
aquatic respiration.1 
! Latreille, though holding the Limuli to be Crustacea, and not Arach- 
niaa, was the first to insist on the branchia-like character of the Scorpion’s 
lung-books 
