CRYSTALLOIDS. 



[ 219 ] 



CTENOSTOMATA. 



ference to works specially devoted to the 

 subject. 



BIBL. Schmidt, Enttv. em. allg. Untersuch. 

 fyc. ; Robin and Verdeil, Chimie Anatom. 

 $c. ; Phillips, Intr. to Mineral. (Brooke 

 and Miller) ; Dana, Mineral. ; Naumann, 

 Elem. d. Min. ; Nicol, Man. of Miner. ; 

 Rammelsberg, Krystallkunde ; Nageli & 

 Schwendener, Mikr. 478. 



CRYSTALLOIDS. These bodies have 

 beennoticed under CHALK and COCCOLITHS. 

 The term has been more recently ex- 

 tended to certain bodies formed of the 

 protoplasmic contents of vegetable cells, 

 which assume crystalline forms, and exhibit 

 the facets and polarizing properties of 

 crystals, yet possess resemblances to organic 

 cell-structures. They are usually colourless, 

 sometimes coloured, the colouring matter 

 being removeable. They swell with re- 

 agents, and consist of two substances of 

 different solubility. They are found in the 

 cell-nuclei of Lathrea, the cells of the skin 

 of the potato, in seeds, and in aleurone- 

 grains (page 28, fig. 66). 



So that we now have 3 kinds of crys- 

 talloids : Ehrenberg's chalk- and concre- 

 tionary crystalloids ; the vegetable crystal- 

 loids ; and Graham's (dialytic) crystalloids 

 =true crystalline matter. 



BIBL. Hartig, Bot. Zeit. 1856, 262; 

 Badlkofer, Kryst. prot. 1859 ; Nageli, Bay. 

 Ak. 1862, 233; Sachs, Bot. 50; Rodwell, 

 Diet. So. 162. 



CRYSTALS. Crystals are constantly 

 met with in the examination of animal 

 and vegetable products ; and the determina- 

 tion of their nature or composition is often 

 of great importance. 



There are five methods of ascertaining 

 this : 1, by ascertaining the atomic weight 

 of the substance, or by its quantitative ana- 

 lysis ; 2, by the study of its crystallographic 

 properties ; 3, by its qualitative analysis ; 

 4, by its spectroscopic analysis; 5, by its 

 polariscopic 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 crystallography. 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. xlii ; the 

 fourth is indispensable in many cases, bu1 

 requires expensive apparatus and great prac- 

 tice ; the fifth is only partially applicable. 



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 relatively constant. In many ani- 

 mal and other liquids, the forms assumed by 

 the crystals deposited are tolerably charac- 

 teristic, so that their composition may be 

 inferred ; but where accuracy is required, it 

 is always well to use chemical reagents. 

 See RAPHIDES. 



The cavities in topaz and other mineral 

 crystals were shown years ago by Brewster 

 to enclose a liquid, crystals, or even a va- 

 cuum. This subject has been further in- 

 vestigated by Sorby and Rutley in rocks, 

 stones, lava, &c., and important geological 

 conclusions have been deduced therefrom. 

 Attention has also been drawn to the cavi- 

 ties containing air or vapour in artificial 

 crystals, and to the crystals formed in blow- 

 pipe beads. 



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 

 cannot be witnessed than the very formation 

 itself taking place under the 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. Sorby, Geol. Jn. xviii. ; id. (blow- 

 pipe beads) Mn. Mic. Jn. i. 349 ; and Jn. 

 Mic. Soc. 1878, i. 1; Guy, Mic. Trans. 

 1868, 1 ; Davies-Matthews, Mounting, 111 ; 

 also CHEMISTRY, CRYSTALLOGRAPHY, and 

 ROCKS. 



CTENOSTO'MATA. A suborder of 

 Infundibulate Polyzoa (Bryozoa). Distin- 

 guished by the cell-orifice being surrounded 

 by a fringe of bristles (more or less deve- 

 loped) when the animal is protruded. 

 Families : 



Alcyonidiidce. Polypary sponge-like, 

 fleshy, irregular in shape ; cells immersed, 

 with a contractile orifice. 



Vesiculariidce. Polypary plant-like, horny, 

 tubular ; cells free, deciduous, the ends 

 flexible and invertible. 



PedicellinidcB. Polypary plant-like, creep- 

 ing, adherent, sending up at irregular 

 intervals free, erect, stalked bodies, without 

 distinct cells. 



Flustrettidee. Cells immersed in a gela- 

 tinous crust, orifice bilabiate. 



