CRYSTALLOIDS. 



L 1*77 ] 



CULICIDJi:. 



balsam ; where this cannot be effected, the 

 crystals should be immersed in liquid, and 

 made to assume the required positions by 

 moving the cover with the mounted needle. 

 BiBL. Schmidt, Entw. eiii. ally. Untersuch. 

 S)'C. ; Robin and Verdeil, Traite de Chimie 

 Anatom. Sec; Phillips, Elementary Tntroduct. 

 to Mineral. (Brooke and Miller); Dana, Syst. 

 of Mineral.; Naumann, Element, d. Mineral.; 

 Nicol, Man. of Mineraloyy ; Rammelsberg, 

 Lehrbuch d. Krystallkunde. 



CRYSTALLOIDS.— These bodies have 

 been noticed under Chalk. Ehrenberg's 

 explanation of their nature appears doubtful; 

 at all events, we do not recollect having ob- 

 served any such bodies among the varied 

 forms assumed by imperfectly crystallized 

 substances. It would be interesting to de- 

 termine whether similar bodies are met with 

 in calcareous strata now in progress of for- 

 mation. 



BiBL. Ehrenberg, Abh. d. Berlin Akad. 

 1848; id. Mikro-Geoloyie. 



CRYSTALS. — Crystals are constantly 

 being met with in the examination of animal 

 and vegetable products, and the determina- 

 tion of their nature or composition is always 

 of great importance. 



There are three methods of determining 

 this : 1, by ascertaining the atomic weight of 

 the substance, or by its quantitative analysis ; 

 2, by the study of its crystallographic pro- 

 jjcrties ; and 3, by its qualitative analysis. 



The first belongs to the domain of che- 

 mistry, and requires an appreciable quantity 

 of substance. 



The second requires well-formed crystals, 

 and a knowledge of crystallograjihy. As the 

 latter is an exceedingly difficult science, re- 

 course is generally had to the third method, 

 upon which some remarks have already been 

 made in the Introduction, p. xxxvii. 



The forms of crystals vary according to 

 the conditions under which they are pro- 

 duced, but there can be no doubt that under 

 absolutely the same conditions, their forms 

 would be relativeh' constant. In many ani- 

 mal and other liquids, the forms assumed by 

 the crj'stals deposited are tolerably charac- 

 teristic, so that their composition may be 

 inferred ; but where accuracy is required, it 

 is alwavs well to use chemical reao:ents. 



Crystals, when rapidly formed, constitute 

 beautiful microscopic objects; the arbores- 

 cent, radiating, and other appearances which 

 they present are well known ; and a more 

 exquisitely curious and interesting sight can- 

 not be witnessed than the very formation 



itself taking place under the microscope. 

 This may be readily seen in a drop of any 

 saline solution spontaneously evaporating 

 upon a slide. See Uric acid and Polar- 

 ization; and for crystals in plants, Ra- 



PHIDES. 



BiBL. See Chemistry, and the Bibl. of 

 that article; also Crystallography. 



CUCULLANUS, Mull.— A genus of En- 

 tozoa, belonging to the order Coelelmintha, 

 and family Nematoidea. 



Char. Body elongate, posteriorly attenu- 

 ate ; head broad, with a bivalve manducatory 

 apparatus ; mouth anterior, terminal, form- 

 ing a long vertical fissure. 



C. eleyans. Found in the intestine, sto- 

 mach, and pyloric appendages of the perch 

 and other freshwater fishes. Almost all the 

 other species of this genus live also in the 

 intestines of fishes. Length 1-6 to 1-3". 

 Colour, reddish-yellow. 



BiBL. Dujardin, Hist. nat. d. Helminthes, 

 p. 245. 



CUCURBITARIA, Grev. See Sph^ria. 

 CULEX, Linn. — A genus of Dipterous 

 Insects, of the family Culicidae. 



Char. Palpi longer than the proboscis in 

 the male, very short in the female. 



Twenty species. C. pipiens, the common 

 gnat. See Culicidae. 



CULICID.E.— A family of Dipterous In- 

 sects, as the type of which the common gnat 

 ( Culex pipiens) may be examined. 



The parts of the mouth are produced into 

 a slender, elongated rostrum or jn-oboscis, 

 which is nearly half the entire length of the 

 insect, and slightly thickened at the tip. 

 This proboscis, simple as it appears, in reality 

 consists of seven pieces in the females, be- 

 sides a pair of many -jointed palpi, which are 

 as long as, or even longer than the rostrum 

 in some of the males, and verv hairv at the 

 extremity ; in the females, however, thej^ are 

 generally very short. The head is small. 

 The antenna) are slender and filiform, as 

 long as, or longer than the thorax, and 

 14-jointed in both sexes ; but they are ])lu- 

 mose in the males (PI. 26, fig. 21) and pilose 

 in the females (PI. 26. fig. 30 a); the basal 

 joint is subglobose and tubercular in form. 

 The eyes are lunate; the ocelli obsolete. 

 The thorax is oblong-oval. The abdomen is 

 long and slender, upon which the wings are 

 incumbent when at rest ; the latter have the 

 veins furnished with scales (PI. 27. fig. 22). 

 The legs are very long and slender. 



The proboscis of the female is composed 

 of the following parts : — 1. An outer tubular 



N 



