GLOSSARY 571 



Spermatogenesis (spur-ma-to-jen'-e-sis), the events leading up to the formation 



of sperm. 

 Sphincter (sfingk'-ter), a muscular band that closes a tube, such as the digestive 



tract. 

 Spicules (spik'-Ols), spiny structures embedded in the bodies of most sponges. 

 Spinneret (spin-er-et'), web-spinning structure found on the ventral surface of 



spiders. 

 Spiracle (spir'-a-kl), body opening associated with respiration, found in insects 



and elasmobranchs. 

 Spleen (splen), a gland found near the posterior portion of the stomach. 

 Sternum (stur'-num), the breast bone. 



Stomodeum (sto-mo-de'-um), embryonic invagination that forms the mouth. 

 Strand (strand), the area between high and low tide marks. 

 Striated (strl'-at-ed), bearing striations, used in referring to muscle fibers bear- 

 ing delicate cross and longitudinal lines. 

 Suture (su'-tur), the point of junction of bones at an immovable joint; to sew 



together. 

 Symbiosis (sim-bi-o'-sis), the association of two living organisms for their 



mutual benefit. 

 Synovial (sin-o-vi-al), referring to movable bone joints. 

 Syrinx (sir'-Inx), an enlargement of the trachea of birds; the sound producing 



apparatus. 

 Systemic (sis-tem'-ik), pertaining to the body generally. 



Tarsal (tar'-sal), an ankle bone. 



Tarsus (tar'-sus), the ankle bones of vertebrates ; the distal segments of the legs 



of insects. 

 Taxonomy (tax-6n'-o-mi), a phase of biology dealing with classification of living 



organisms. 

 Telophase (tel'-o-faz or te'-lo-faz), the last stage of mitosis. 

 Telson (tel'-sun), the fan-shaped structure on the posterior end of crayfish and 



lobsters. 

 Tendon (ten'-dun), a tough, elastic fiber connecting a muscle to a bone. 

 Testosterone (test-Ss'-ter-6n), male hormone secreted by the testes. 

 Testis (tes'-tis), pi. testes, the male gonad; the gland that produces sperm. 

 Theory (the'-o-n), a scientific assumption, usually considered to have more 



weight of evidence supporting it than an hypothesis. 

 Thoracic (tho-ras'-ik), pertaining to the chest. 

 Thorax (tho'-rax), the chest region of an animal body. 

 Thrombocyte (thr6m'-b5-sit), blood platelet. 



Thyroxin (thi-rox'-in), the hormone produced by the thyroid gland. 

 Tibia (tib'-i-a), the larger of the bones of the lower leg; also a segment of insect 



legs. 

 Tissue (tis'-su), a group of similar cells together with the intercellular matrix 



that surrounds them. 

 Trachea (tra'-ke-a), the tube carrying air from the larynx to the branchial tubes 



in most air-breathing vertebrates. 

 Trichocyst (trl'-ko-sist), tiny bulbs of a gelatinous liquid that may be expelled 



to form sticky threads in certain protozoa. 

 Triploblastic (trip-lo-blas'-tik), having three germ layers in the body. 



