SEX- 



291 



SIM- 



Pert, sex ; appl. reproduction, opp. 

 asexual (bio/.). 



sexual cell, an ovum or sperm, 

 sexual dimorphism, strongly- 

 marked differences, in size, colour, 

 etc., between male and female of 

 one species (soot.}. 

 sexual generation, a gamobium 

 or medusa. See alternation of 

 generations. 



shaft (shaft) n. [A.S. sceaft, a spear- 

 shaft.] A rachis ; the distal part 

 of the stem of a feather; the straight 

 cylindrical part of a long bone 

 (zool.}. 



sheath (sheth) n. [A.S. sceth, shell 

 or pod.] A protective covering ; 

 a theca ; an investing petiole (dot.} ; 

 an insect wing-cover (zool.}. 

 shell (shfil) n. [A.S. scell, shell.] The 

 hard outer covering of animal or 

 fruit (bio/.} ; a covering, calcareous, 

 siliceous, bony, horny, or chitinous 

 (zool.}. 



shell gland, shell sac, the organ 

 in whose walls material for forming 

 a shell is created. 



shield (sheld) n. [A.S. scild, a 

 shield.] A protecting structure 

 such as a carapace or lorica 

 (zool.}. 



shoulder blade, the scapula. 

 shoulder girdle, the pectoral girdle, 

 which consists of scapula, coracoid, 

 and clavicle (anat.}. 

 sialoid (si'aloid) a. [Gk. sialon, 

 saliva ; eidos, resemblance.] Like 

 saliva (phys.}. 



sicula (sik'ula) n. [L. sicula, a small 

 dagger.] A small dagger-shaped 

 body at the end of a Graptolite, 

 supposed to be the skeleton of the 

 primary zooid of the colony (pal.}. 

 side-chain theory, Ehrlich's theory 

 of the phenomena of immunity, viz., 

 that toxins unite with living proto- 

 plasm by possessing the same 

 property as that by which nutritive 

 proteins are normally assimilated 

 (phys.}. 

 sieve cell, the thin-walled elongated 



cell of a sieve tube (bot.). 

 sieve disc or plate, the end walls 

 of sieve cells thickened and modi- 

 fied to form sieve-plates (bot.}. 

 sieve pit or pore, a perforation of a 

 sieve-plate (bot.}. 



sieve tissue, the /essential tissue of 

 the phloem of vascular bundles 

 (bot.}. 



sieve tubes or vessels, long slender 

 structures consisting of elongated 

 cells placed end to end, developed 

 in Angiosperms as lines of con- 

 duction of food (bot.}. 



sight (sit) n. [A.S. siht, sight.] The 

 visual faculty ; impressions of out- 

 ward things conveyed to the brain 

 by means of retina and optic nerves 



sigiUate (sij'ilat) a. [L. sigillum, a 

 seal.] Having seal-like markings, 

 as certain roots (bot.}. 

 sigma (slg'ma) n. [Gk. 2, sigma.] 

 A C-shaped sponge spicule (zool.}. 

 sigmaspire (sig'masplr) n. [Gk. 2, 

 sigma ; L. spira, a coil.] A sigma 

 with an additional twist (zool.}. 

 sigmoid (sig'moid) a. [Gk. 2, sigma ; 

 eidos, resemblance.] Curved like a 

 sigma ; curved in two directions ; 

 appl. arteries, cavities, valves 

 (anat.}. 



sigmoid flexure, an S-shaped double 

 curve as in a bird's neck ; the S- 

 shaped curve described by the 

 intestine (anat.}. 



silicle (sll'ikl) n. [L. silicula, a little 

 pod.] A silicula, or very short flat 

 form of siliqua (bot.}. 

 silicular (silik'ular) a. [L. silicula, a 

 little pod.] Siliculose ; siliculous ; 

 like or pert, or having a silicle (bot.}. 

 siliqua (slllk'wa) n. [L. siliqua, a 

 pod.] A long cylindrical fruit 

 divided in two by a false septum, 

 characteristic of the Cruciferae 

 (bot.}. 



silique (silek'), a siliqua. 

 siliquiform (sTlik'wiform) a. [L. 

 siliqua, a pod ; forma, shape.] 

 Formed like a silique (bot.}. 

 siliquose (sil'ikwos) a. [L. siliqua, 

 pod.] Siliquous ; bearing siliques 

 (bot.}. 



simian (slm'Ian) a. [L. simia, an 

 ape.] Possessing the characteris- 

 tics of or pert, the anthropoid apes 

 (zool.}. 



simple eyes, ocelli which occur with 

 or without compound eyes in the 

 adults of many Insects ; usually the 

 only eyes possessed by larvae ; 

 eyes with only one lens (zool.}. 



