SLATE. 



[ 698 ] 



SNOW. 



arrangement, in injected preparations, some 

 of which, OS thuse of the pulp of the finger, 

 form very beautiful objects. The epidermis 

 is easily separated by maceration. 



Fig. 645. 



Per-Hon of the skin of tlie heel parallel to the siirfnce, 

 through one entire ridge of the skin and part of two 

 others ; showing tha arrangement of the papillse in rows 

 corresponding to the ridges of the cutis, a, cuticle 

 between the ridges; h, rete mueosum ; c, papillae; d, 

 portion of the rete mueosum between papillae arising 

 from a common base ; e, sudoriparous ducts. 



Magnified 60 diameters. 



The integument of animals is noticed 

 under the respective heads of the classes. 



It must be remarked that the terms epi- 

 dermis and cuticle are generally used syno- 

 nymously. 



BiBL. KiJlliker, Mik. An. i., and Geivebe- 

 lehre ; Todd and Bowman, Phys. An.; 

 Meissner, Beifr. z. An. ti. Phys. cl. Haut, 

 1863 ; Biesiadecki, Strieker's Hist. 



SLATE. See Rocks. 



SMARIS, or Smaridia, Latr. — A genus 

 of Acarina, family Trombidina. 



Char. Palpi slender, inserted upon a re- 

 tractile rostrum ; mandibles sword-shaped ; 

 body entire, narrow anteriorly ; coxse stout, 

 distant, the anterior articulated to a fixed 

 eminence upon the body ; legs palpatorial, 

 u.sed also as palpi, the anterior longest. 



S. jMpil/osa (PI. 6. fig. 36; a, mandible). 

 Body vermilion-coloured, broader in front, 

 depressed, covered with short cylindrical 

 papillfe rounded at the end. Fusiform 

 scales replace the papilhx; upon the legs, 

 palpi, and rostrum. 



Found upon the trunks of trees, and in moss. 



Several other species are found in moss, 

 upon fallen leaves, and on the debris left 

 after inundations. 



In S. expalpis, Koch, there are no palpi. 

 BiBL. Duges, Ann. Sc. N. 2. i. 16 & 34; 

 Clervais, Walckenaer' s Apt. iii. 173; Murray, 

 Ec. Ent. 149. 



SMIT'TIA, Hincks. — A genus of Esclia- 

 ridae (Cheilostomatous Polyzoa),=iey«"a^m 

 sp., with the secondary orifice elevated, pro- 

 duced, and channelled in front. 7 species. 

 (Hincks, Polyzoa, 340.) 

 SMUT. See Uredo. 

 SNAILS, WATER-.— Most microscopic 

 observers, ever anxious to determine the 

 unknown cau.se of the curious circulation 

 or rotation (Rotation) taking place in cer- 

 tain water-plants, as Vallisneria., Anacharis, 

 &c., keep these growing in large glass ves- 

 sels, as confectioners' jars, or Vivaria. 

 These plants, and the sides of the vessels, 

 are however very apt to become overgrown 

 and obscured by Coufervoid Algae (as CEclo- 

 gonium), Palmellaceae, &c., which ma^^ be 

 prevented by keeping water-snails in the 

 water, as species of Limttcetis, Physa, By- 

 thinia, Phmorhis, &c. The latter are best 

 for this purpose (the shell is flat-spiral). 

 If Desmidiaceas, Diatom aceae. Infusoria, &c. 

 are to be preserved, the snails must be care- 

 fully excluded, because many of these are 

 consumed by them, and will not live, as the 

 bottom of the vessels soon becomes covered, 

 when snails are kept, with a load of excre- 

 ment. The chanvcters of the snails are too 

 long to be given here. The gelatinous masses 

 of ova are found adhering to water-plants. 

 See the Bibl. of Mollusca. 

 SNOW. — The various forms presented by 

 ice or crystallized water in the form of snow 

 constitute beautiful although fugitive mi- 

 croscopic objects. 



The crystals belong to the rhombohedric 

 or hexagonal system. Several hundreds of 

 forms have been observed, and many of 

 them figured. Among them may be men- 

 tioned hexagonal or dodecahedral plates ; 

 hexagonal prisms, single, arranged in a 

 stellate form, or terminated by rectangularly 

 placed plates or secondary groups of needles; 

 hexagonal pyramids. Sec. The angles of 

 these forms frequently constitute secondary 

 centres, around which other similar or dis- 

 siuiilar forms are aggregated. By some 

 authors these forms are regarded as skeleton 

 crystals. 



See also Red Snow. 



Bibl. Scoresby, ^nf/c Begions; Kamtz, 



