894 CRANK. 
CRAWFISH. 
the strongest of their number, whose trumpet- | baceous species; and these are distributed among 
like voice is heard as if directing their advance, 
when the flock is far above the clouds, and en- 
tirely out of sight. To this call-note of the leader 
the flock frequently respond by a united clangour, 
which, heard at such a distance, does not pro- 
duce an unpleasing effect. From the sagacity 
with which these birds vary their flight, accord- 
ing to the states of the atmosphere, they have, 
from the earliest ages, been regarded as indicators 
of events; and their manoeuvres were attentively 
watched by the augurs and aruspices—a circum- 
stance which, together with their general harm- 
lessness and apparent gravity of demeanour, led 
to their being held in a sort of veneration, even 
by some civilized nations. When obliged to take 
wing from the ground, cranes rise with consider- 
able difficulty, striking quickly with their wings, 
and trailing their feet along and near the ground, 
| until they have gained a sufficient elevation to 
commence wheeling in circles, which grow wider 
and wider, until they have soared to the highest 
regions of the air. When their flight is high and 
| silent, it is regarded as an indication of continued 
fine weather ; they fly low and are noisy in cloudy, 
wet, or stormy weather. 
CRANE’S-BILL. See Gerantum. 
CRANK. An iron axis with the end bent like 
an elbow, for the purpose of moving a piston, the 
saw in a sawmill, &c., causing it to rise and fall 
at every turn; also for turning a grindstone, &c. 
The common crank affords one of the simplest 
and most useful methods for changing circular 
into alternate motion, and wice versa. Double 
and triple cranks are likewise of the greatest use 
for transmitting circular motion to a distance. 
In fact, cranks belong to those few simple ele- 
ments on which the most complicated machines 
rest, and which, like the lever, are constantly 
employed. 
CRANIUM. See Sxuut. 
CRASSULA. A genus of ornamental, green- 
house plants, forming the type of the natural 
order Crassulaceze. This order consists of suc- 
culent plants, some herbaceous, others shrubby, 
some annual, others perennial, and all fleshy in 
their leaves and comparatively dry and arid in 
the character of their favourite situations. Some 
plants of the order may be found wild in almost 
every part of the world; but most occur in hot, 
dry, and exposed spots of the somewhat temper- 
ate portions of the eastern hemisphere, and many 
are at once abundant, conspicuous, and most 
ornamental on the sterile, arenaceous plains of 
the Cape of Good Hope, and on the hot cliffs and 
volcanic wastes of the Canary Islands. Their 
flowers are, for the most part, red, orange, white, 
or yellow, and are arranged in either corymbs, 
cymes, spikes, or panicles, and, in very numerous 
instances, are eminently beautiful. The order 
comprises, within the gardens and open-grounds 
of Great Britain, 8 or 9 hothouse species, about 
180 greenhouse species, and about 90 hardy her- 
22 genera,—the most familiar of which are cras- 
sula in the greenhouse, and sedum and semper- 
vivum in the open air. The hardy kinds, such 
as the sedums and sempervivums, grow on walls, 
rockwork, and other dry situations; and the ten- 
der kinds require to be potted in dry rubbish, 
and to receive little water except during the 
period of full activity. 
' Seven or eight species which were formerly 
comprised in the genus crassula are now assigned 
to other genera; but about 85 described species 
are still ranked as crassulee, and upwards of 50 of 
these have been introduced to the greenhouses of 
Britain. Most of the introduced species have 
such thick, fleshy leaves and stems, as at once to 
evince, to even the unpractised eye, their close 
affinity to our houseleeks and sedums; yet they 
possess a certain delicacy which renders a com- 
parison of them with houseleeks exceedingly vul- 
garizing, and they display in the texture and 
tinting of their flowers such exquisite characters 
as render all of them ornamental, and some of 
them superb. Most are from the Cape of Good 
Hope; about three-fourths are evergreen, under- 
shrubs; about a dozen are annuals; and all the 
perennial kinds are propagated from cuttings, 
and the annual kinds from seeds. Among the 
most handsome are C. ramosa, C. imbricaia, C. 
acutifolia, C. odoratissima, C. tetragonia, C. arbor- 
escens, C. lactea, (. scabra, C. marginalis, OC. per- 
foliata, and C. ciliata ; and among the newest in 
vogue, are C. coccinea, CO. versicolor, and C. nitida. 
CRATAIGUS. See HawrHorn. 
CRAWFISH. A crustaceous genus, belonging 
to the family Decapoda macroura (ten-legged, 
long-tailed), characterized by having the anterior 
part of the elongated, semi-cylindric, superior 
shell produced to form a rostrum or beak ; the 
abdomen large, slightly attenuated posteriorly, 
composed of six joints, forming a tail quite as 
long, when extended, as the body, and terminat- 
ing in five broad-fringed, swimming appendages, 
which fold laterally upon each other. In both 
sexes, the under part of the abdomen is generally 
provided with five pairs of false claws, each ter- 
minated by two plates or plaments. The exte- 
rior jaw-feet are mostly narrow, elongated, and do 
not entirely cover the other parts of the mouth. 
The gills are pyramidal, brush-shaped, or plume- 
like, separated from each other by tendinous slips, 
and situated beneath the sides of the great su- 
perior shell, over the external base of the feet. 
Of the latter, the second and third pairs are 
elongated, slender, and furnished at the last 
joint, which is moveable, with small pincers; the 
fourth and fifth pairs have the last joints simply 
pointed or hooked. The sexual organs are placed, 
in both sexes, in the basal joint of the last pair 
of feet. The species belonging to this genus, as 
at present restricted, do not exceed six. Some 
of these kinds are peculiar to salt and others to 
fresh water. Of the former, the most celebrated 
