856 Appendix 



Sclerotic (skle -rot' ik) (Gr. skleros, hard) , tough, outer coat of eyeball. 

 Scolex (sko'leks) (Gr. skolex, worm), enlarged anterior end of tapeworm. 

 Sebum (L. sebum, tallow), fatty secretion of the sebaceous glands of the skin. 

 Secondary sexual characters, structural, functional, or behavioral differences be- 

 tween two sexes other than those pertaining to the different sex organs 



themselves. 

 Secretin (se -kre' tin) (L. secratio, secrete), intestinal hormone which activates the 



pancreas. 

 Secretion (se kre' shun) (L. secretus, to separate), producing a substance by the 



action of a gland or cell. 

 Sedentary (sed'enteri) (L. sedere, to sit), temporarily attached and not entirely 



free moving. 

 Segmentation (seg men -ta' shun), i^^ Metamerism. 

 Segmentation cavity, hollow, central cavity (blastocoele) formed during early 



cleavage of embryo. 

 Segregation law, passage of one member of each pair of allelomorphic genes to 



different germ cells during maturation. 

 Selective absorption, absorption of certain substances and not others. 

 Self-fertilization, fertilization (fusion) of an egg by a sperm from the same indi- 

 vidual. 

 Semicircular canals (L. semi, half; circulus, circle), ear canals of vertebrates 



devoted to sense of equilibrium. 

 Seminal receptacle (sem' i nal) (L. semen, seed fluid; recipere, to receive), organ 



for storing sperm from opposite sex until needed for fertilization. 

 Seminal vesicle (sem' i nal) (L. semen, seed fluid; vesica, bladder), saclike organ 



for storing sperm during spermatogenesis, as in earthworm. 

 Seminiferous tubule (sem i -nif er us) (L. semen, seed fluid; jerro, to carry; 



tubules, small tube), tube to conduct seminal fluid of male. 

 Semipermeable, permitting passage of certain molecules but not others. 

 Sepal (se' pal) (L. separ, covering), one of the outer whorl of floral leaves which 



taken as a group are known as the calyx. 

 Septum (plural septa) (sep' tum) (L. septum, partition), partition separating two 



cavities. 

 Serial homology (ho-mol'oji) (Gr. homo, similar; logos, study), presence of 



structures of similar origin and form on different segments of the same 



animal. 

 Serous (se' rus) (L. serum., watery), clear, watery fluid. 

 Sertoli cells (ser-to'le), modified, supporting or nurse cells for forming sperm 



in the testes. 

 Sessile (ses' il) (L. sedere, to sit), permanently attached and never free moving. 

 Seta (plural setae) (se' ta) (L. seta, bristle), bristelike structure. 

 Sex chromosomes, odd chromosomes (X and Y chromosomes) distinguished from 



the regular chromosomes which aid in sex determination. 

 Sex-limited characters (sex-influenced), those traits influenced or modified by the 



presence of a particular sex organ (and its secretion), such as beard and 



voice of the male due to hormones from the male testes. 

 Sex-linked characters, those traits whose genes are located in the sex chromosome. 



