726 Reviews. [ Oct., 
by the falces, usually but improperly termed mandibles, which are 
terminated by a pointed fang, having a ginglymoid movement, and by 
the oral apparatus. Hight legs of seven joints each, having two or 
more claws at their extremity, are articulated round the cephalo- 
thorax, to which the abdomen, covered with a leathery or horny plate, 
is united by a short cartilaginous pedicle. Of course the spinning 
organs claim especial attention, consisting of four, six, or eight mam- 
mule, situated immediately below the anus, and each composed of one 
or more joints, from the terminal joint of which five movable papille 
arise, whence issues the viscous secretion of which the silken lines 
produced by spiders are formed. These are connected with special 
organs for the formation of this secretion, consisting of intestiniform 
vessels, having at their base some small supplementary canals. The 
viscous substance hardens immediately on exposure to the air, forming 
delicate filaments, which unite to form a common thread. 
The falces are used for seizing, killing, and retaining the prey ; 
but a remarkable function is claimed for the palpi. In male spiders, 
the digital joint of these organs, which are situated on the maxille, 
is commonly short, oval, and dilated, and have the sexual organs 
(which are thus double) attached within and partially concealed by a 
cavity on its under side. This view of the nature of the palpi was 
adopted by Lister, and recent researches, conducted with the utmost 
caution, have clearly established the accuracy of the opinion. In the 
females, the palpi are for the most part terminated by a curved pecti- 
nated claw. 
Spiders change their skins several times before they reach 
maturity, after each process remaining for a short period in a state of 
great exhaustion. So also, like Crustacea, they have the power of 
reproducing detached or mutilated limbs, palpi, or spinners, but only 
at the period of moulting. Such a mutilated leg may be renewed four 
or even six times consecutively during the period of immaturity. 
The ingeniously-constructed nets or webs which are so familiarly 
known to all are of several kinds, characterizing different groups of 
spiders; some of these have not much pretension to elegance of 
design, but nevertheless well fulfil the purpose of a snare, for which 
they are intended. The circular geometric nets of the Hpéire, how- 
ever, are really wonders of art. An elastic spiral line thickly studded 
with minute globules of viscid gum, whose circumvolutions are crossed 
by radii converging to a common centre, and apparently formed of a 
different material, being unadhesive and very much less elastic. So 
also the central convolutions are free from the adhesive material, and 
these form a look-out station from which the spider may keep watch. 
With regard to the viscidity of the spiral web, light has been thrown 
upon its nature even since the publication of Mr. Blackwall’s work, 
the first part of which appeared in 1861. He there calculates that the 
minute globules which stud the lines and give rise to the viscidity are 
so closely ranged as to give an average of twenty globules upon one- 
tenth of an inch; and basing upon this calculation, he finds that a 
large net of Hpéira apoclisa, 14 or 16 inches in diameter, contains 
upwards of 120,000 viscid globules, and yet the spider will complete 
