550 



CRAYFISH 



CREAM 



by venous channels to the gills, and thence back 

 again to the heart. The respiratory system includes 

 twenty pairs of feathery gills lying under the 

 shelter of the sides of the great shield. The cease- 

 less baling inovement of one of the mouth append- 

 ages secures a current of water. The excretory 

 system is represented by a ' green-gland ' or kidney, 

 lying behind the base of the antennae, on which 

 its opening, shielded by a prominent knob, may be 

 readily seen. The reproductive system consists of 

 three-lobed essential organs with paired ducts 

 opening on the thoracic legs. 



The eggs are laid in November or December, and 

 are glued by a secretion to the abdominal legs of 

 the mother. The young ai-e hatched in May to 

 July. They do not differ in any important features 

 from the adults, and the crayfish has thus very 

 much abbreviated the typical life-history. The 

 young escape from the inclosing egg-cases, to 

 which they, however, adhere for a while by means 

 of the strongly incurved claw-tips. The female 

 with its crowd of attached young presents a curious 

 and interesting appearance. The young crayfish 

 moults eight times during its first year of life, five 

 times in the second, twice in the tliird. The male 

 is adult in its third year, and continues for some 

 time at anyrate to moult twice a year. The female 

 is mature in the fourth year, and has only one 

 annual moult. The moulting is in part the result 

 of the fact that the inclosing armature does not 

 grow with the growth of the body. Reserve pro- 

 ducts of lime and glycogen accumulate before 

 moulting ; the old shell virtually dies ; a new 

 armature ( at first soft ) begins to be formed ; the 

 animal grows ; the old husk, including the hard 

 structures of the stomach, is cast ; and the crayfish 

 is left perfectly limp and helpless. The fatigue 

 of the process is shown in the great mortality. 



The crayfish is exclusively a fresh-water form, 

 barring the fact that some related genera ( Engaeus, 

 Cambarus, Parastacus ) appear to be for the most 

 part terrestrial. They usually make burrows by 

 the sides of streams, and often lie at the mouths 

 of their holes in wait for passing prey. They are 

 chiefly nocturnal. In their diet they are strikingly 

 omnivorous, eating most things available, from 

 worms to water-voles. Dead animals, molluscs, 

 worms, and insect larvae form their chief sources 

 of supply. In captivity they may be kept for a 

 while on bread crumbs. In certain cases they do 

 not refrain from eating one another. Their chief 

 enemies are said to be eels and otters. 



Crayfishes, though fresh-water forms, have a 

 peculiarly wide distribution. The English and 

 Irish crayfish is a variety of A. fluviatMs, and is 

 by authorities designated A. torrentium. It occurs 

 all over Europe, except in Scandinavia and Scot- 

 land, but is locally limited by the presence of suffi- 

 cient lime in the water for shell -form ing purposes. 

 Another variety of A. fluviatilis, A. nobilis, is also 

 widely distributed on the Continent. This variety 

 is much cultivated in France and elsewhere for 

 the sake of its dainty though not abundant flesh. 

 They are in best condition from May to August. 

 In ponds for artificial breeding, the animals often 

 fall victims to disease, probably of a fungoid char- 

 acter. In rivers they are sometimes netted, some- 

 times lured by a light in the darkness. Numerous 

 other species occur both in the Old and New 

 World, and along with the southern forms (Par- 

 astacidae) may be fairly called cosmopolitan. In 

 the United States, where they are very common, 

 their burrows sometimes cause crevasses or ruptures 

 in the artificial dykes of rivers. The largest species 

 measures over a foot in length. Crayfish-like forms 

 appear in the Middle Mesozoic times, and a some- 

 what doubtful Astacus (A. philippi) has been found 

 in the carboniferous limestone of Ireland. It is 



probable that they were originally marine. The 

 term crayfish is often extended to the nearly re- 

 lated marine form, the Norway Lobster or Nephrops 

 norvegicus (see LOBSTER). See Huxley's Crayfish: 

 an Introduction to Zoology (Inter. Sc. Series, 

 1877). 



Crayon ( Fr. , 'a pencil ' ). Though used in 

 French, and occasionally in English, to designate 

 pencils generally, including those made of lead, the 

 word crayon is more frequently applied in England 

 to those small cylinders of charcoal, or of pipe- 

 clay or chalk coloured with various pigments, 

 which are used for drawing. Cohesiveness is given 

 to the paste of Avhich the cylinders are formed by 

 means of gum, wax, soap, &c. Crayon drawings 

 are often remarkable for the delicacy and softness 

 with which objects are represented, but they ars 

 deficient in power. See PENCIL, CHALK. 



Cream is the fat of Milk (q.v.). It exists in 

 minute globules throughout the bulk of milk 

 as it comes from the cow. In virtue of being 

 lighter than the watery portion of milk, cream 

 gradually rises and forms a thin yellowish greasy 

 layer on the surface. Devonshire cream, or clouted 

 (i.e. clotted) cream, is obtained by heating milk 

 in a shallow wide pan on a hot plate or over a slow 

 charcoal -fire. The milk should stand in the pan for 

 twenty-four hours before heating. It usually takes 

 from half an hour to three-quarters of an hour to heat 

 the milk completely ; but it must not boil. It then 

 stands for twenty-four hours, when the cream is 

 skimmed off, and a little sugar thrown on the top. 

 Whipped cream is cream or milk beat up with 

 white of egg by means of a whisk. Lemon cream, 

 Vanilla cream, &c. are made with milk, white of 

 egg, and sugar, and flavoured. Cream cheese may 

 be made of rich cream, or cream, milk, and rennet, 

 tied up in a clean wet cloth, and kept for some 

 days in a cool place, then put in a finer cloth, and 

 placed for a day or two in a mould, with a weight 

 upon it. The term cream is used frequently for 

 anything superior in quality ; thus the French, in 

 referring to persons in the height of fashion, speak 

 of La creme de la cre~me, ' the cream of cream. ' 



CREAM SEPARATORS (Centrifugal). The best- 

 known forms are the 'Laval,' the 'Danish,' and 

 the ' Victoria ' the latter a recent invention of a 

 Glasgow firm. Though they differ in form and in 

 detail, the principle involved in the work of separ- 

 ating the butter is common to all. Advantage 

 is taken of the difference existing between the 

 specific gravity of cream and the watery part of 

 milk. While yet warm the milk coming from the 

 cow is run into a strong, spherical, steel vessel 

 revolving at high speed. As the milk is carried 

 round within the vessel (whether revolving hori- 

 zontally or vertically) it rises up the sides and 

 stands as a wall, thus forming a lining of milk 

 while the speed is maintained. The heavier part 

 inclines outwards, and the light cream is forced 

 inwards and forms an inner layer. From the 

 positions indicated the separated cream and milk 

 are conducted into different channels, and finally 

 into different vessel receptacles. The advantages, 

 as compared with the old method of flat setting 

 (see MILK), are that the cream is got off im- 

 mediately ; no time is allowed for the development 

 of acidity in either the skim milk or cream, and 

 more of the cream present can be removed the 



Sroportion being as 13 is to 11. Small machines 

 riven by hand, costing 13, and separating 12 

 gallons of milk an hour, do not give quite so good 

 results as those driven by steam. Prices range, 

 for those of sizes capable of separating 45 to 150 

 gallons of milk an hour, from 24 to 45. A 

 steam turbine has recently been adopted as the 

 means by which power is communicated. The 



