Appendix 857 



Sexual dimorphism (dl -mor' fizm) (Gr. di, two; morphe, form), two forms or 

 types of a plant or animal due to their sex. 



Sieve tube, elongated, fused, conducting cells of plant phloem which have per- 

 forated sieve plates at their ends. 



Sigmoid (sig'moid) (Greek letter, sigma;. eidos, resemble), curved like the Greek 

 letter sigma. 



Sinus venosus (si' nus ve -no' sus) (L. sinus, cavity; vena, vein), thin-walled cham- 

 ber in certain hearts into which main veins empty. 



Smooth muscle, one whose cells are not striated. 



Sol, a state of a colloidal system in which the external phase is more liquid than 

 the internal phase (contrast with Gel). 



Solation (so -la' shun), phenomenon of forming a sol. 



Soma (so' ma) (Gr. soma, body), entire body, exclusive of reproductive cells. 



Somatogenic reproduction (so mat o -jen' ik) (Gr. soma, body; genesis, origin), 

 reproduction by division of a multicellular body by fission, budding, etc. 

 (contrast with Cytogenic reproduction). 



Somatoplasm (so -mat' o plazm) (Gr. soma, body; plasma, liquid), protoplasm of 

 the body (somatic) cells. 



Somite (so' mite), segment or metamere of an organism. 



Sorus (sor' us) (Gr. sorus, heap), a heap of sporangia as on fern leaves. 



Special creation, doctrine that each species of organism is specially created. 



Species (spe'shes) (L. species, particular kind), individuals so similar that they 

 might appear to have originated from the same parents. 



Sperm, see Spermatozoa. 



Spermatheca (sperm a -thek' a) (Gr. sperma, sperm; theke, case), saclike struc- 

 ture of certain invertebrates for storing sperm. 



Spermatia (spur -ma' she a) (Gr. sperma, seed), cells in rust fungi, produced in 

 spermagonia; also the male gamete of red algae. 



Spermatid (sperm a -tid') (Gr. sperma, sperm), male cell arising by division from 

 a secondary spermatocyte and which later gives rise to a sperm. 



Spermatocyte (sper -mat' o site) (Gr. sperm, sperm; kytos, cell), male germ cell 

 (arising from the spermatogonium) before it is mature. 



Spermatogenesis (sper mat o -jen' e sis) (Gr. sperm, sperm; genesis, origin), for- 

 mation of mature sperm. 



Spermatogonium (spur mat o -gon' i um) {Gr. gonos, offspring), primordial male 

 cell giving rise to the spermatocyte; flask-shaped structure in rust fungi, 

 producing spermatia. 



Spermatozoa (spur ma to -zo' a) (Gr. sperma, sperm; zoa, animal), male sex cells 

 (sperm) . 



Sphenopsida (sfen -op' si da) (Gr. sphen, wedge; opsis, appearance), subphylum 

 including horsetails. 



Sphincter (sfingk' ter) (Gr. sphinggein, to bind tightly), circular muscle to close 

 an opening, as the stomach, bladder, anus, etc. 



Spinal canal, canal in the spinal column containing the spinal cord. 



Spinal column, bony structure enclosing spinal cord. 



Spindle (A.S. spinnan, to spin), fibrous structure of nucleus associated with 

 chromosomes during mitosis. 



