524 GLOSSARY 



Serial homology (ser'i al ho mol'o ji), presence of structures of similar origin 



and form in different segments of the same animal. 

 Serosa (sero'sa), membrane covering peritoneal surface of internal organs; 



one which secretes a watery fluid. 

 Sertoli cells (ser t5'le sels), modified, supporting or nurse cells for forming 



spermatozoa in the testes. 

 Serum (se'rum), the fluid part of the blood which remains after clotting. 

 Sessile (ses'il), attached directly and incapable of locomotion. 

 Seta (se'ta), hairlike spine or bristle, found in animals. 



Sinus (si'nus), a cavity in a bone or other part, or a dilated vessel or canal. 

 Siphon (si'fon), a canal or passageway, as the waterways in clams or tunicates. 

 Somatic cells (somat'ik), the cells of the body exclusive of the germ cells; 



body cells. 

 Somites (so'mits), segments of the body of a segmented animal. 

 Spermatogonium (spur ma to go'nium), a male germ cell during the period of 



multiplication and growth in maturation process. 

 Spermatocyte (spur'ma to sit), the male germ cell before its maturation is 



completed. 

 Spermatogenesis (spur ma to jen'e sis), the maturation of the male germ cells. 

 Spermatozoa (spur ma to zo'a), mature male germ cells. 

 Sphincter (sfingk'ter), a muscular band surrounding a tube or aperture which, 



by its contraction, closes the lumen. 

 Spicule (spik'ul), one of numerous needlelike, solid structures found supporting 



the tissues in the body wall of sponges. 

 Spiracle (spir'ak'l), openings of air tubes in insects, or modified opening of 



first gill slit of certain fish. 

 Spireme (spi'rem) thread, the coiled bead-like string of , chromatin material 



that appears during the prophase of mitosis. 

 Splanchnic (splangk'nik), has reference to the visceral organs. 

 Spongin (spun'jin), the skeletal material of a sponge. 

 Sporulation (spor u la'shun), production of spores by division of a protozoan 



while encysted. 

 Statohlast (stat'6 blast), an encased, asexual winter bud of a bryozoan. 

 Statocysts (stat'6 sists), sense structures assisting in maintaining equilibrium 



in certain forms. 

 Steapsin (steap'sin), one of the pancreatic enzymes which is capable of chang- 

 ing fats to fatty acids and glycerin. 

 Stereohlastula (ster e o blas'tu la), a blastula in which all the cells are in close 



contact and no blastocoele is formed. 

 Stigma (stig'ma), a sensitive pigment spot of Protozoa or the opening of a 



spiracle of insects. 

 Stomatodeum (sto ma to de'um), the opening of the developing alimentary tract 



in an embryo. 

 Stratum (stra'tum), a layer of a series. 



Striated (stri'ated), a type of muscle with more dense areas across the fibers. 

 Strobila (strobi'la), a series of individuals produced by linear budding, as cer- 

 tain Scyphozoa and tapeworms. 

 Succession (suk sesh'un), the successive occupation of a given area by several 



species, either hourly, daily, or seasonally. 

 Sustentative tissue (sus'ten ta tiv), binding together or supporting the various 



parts of the body. 

 Suture (su'tur), to sew together; a line of junction. 

 Symbiosis (sim b! 6' sis), the living together of two organisms for their mutual 



benefit. 

 Synapsis (sinap'sis), the pairing of the chromosomes in the germ cells at one 



stage of maturation. 

 Syncytium (sin sish'i dm), a mass or layer of protoplasm with numerous nuclei 



but without distinct cell boundaries. 



