686 



COLLEGE ZOOLOGY 



before being discharged. They are considered 

 a part of the male genital system. 



Sem'i-nif'er-ous tu'bule (L. semen, seed; ferro, 

 to carry. L. tubulus, small tube) . A tube to 

 conduct seminal fluid. 



Sen'so-ry cell (L. sensus, sense. L. cella, com- 

 partment). A cell that is very sensitive to 

 stimuli; a receptor. 



Sep'tum (L. septum, partition). A partition 

 that separates two cavities or two structures. 



Ser'i-al ho-moro-gy (L. series, join. Gr. homos, 

 same; logos, discourse). Occurrence of 

 homologous structures in different segments 

 of the same individual; homology repeated in 

 a series. 



Se-roro-gy (L. serum, liquid). The study of 

 serums and their action. 



Se'rous (L. serum, liquid). Pertaining to, pro- 

 ducing, or resembling serum. 



Se'rous coat (L. serum, liquid. O.F. cote, coat) . 

 The peritoneal covering of the visceral organs. 



Ses'sile (L. sedere, to sit). Attached; not free 

 moving; sedentary. 



Se'tae (L. seta, bristle). Bristles such as those 

 embedded in the body wall of the earth- 

 worm. 



Sex chro'mo-somes (L. sexus, sex. Gr. chroma, 

 color; soma, body). The X, Y chromosomes 

 especially concerned with the determination 

 of sex. See X, Y chromosomes. 



Sex'u-al di-mor'phism (L. sexualis, of sex. L. 

 dis, indicating separation; Gr. morphe, 

 form). Phenomenon of the two sexes of a 

 given species differing in secondary sexual 

 characters. Many common animals, including 

 mankind, are sexuallv dimorphic. 



Sex'u-al re'pro-duc"tion (L. sexualis, of sex. 

 L. re, again; pro, forth; ducere, to lead). 

 Reproduction invoh'ing a gamete or gametes 

 (sex cell or sex cells). 



shaft (A.S. sceaft, dart). The slender, middle 

 portion of a long bone. 



Si'nus (L., cavity). A thin-walled cavity. 



Si'nus-oid (L. sinus, fold; Gr. eidos, form). 

 Large, irregular, tortuous, blood spaces which 

 are comparable to capillaries in that their 

 walls form an endothelial tube, but thev dif- 

 fer from capillaries in that their lumina are 

 of greater size. 



So'ma (Gr., body). The entire body, exclusive 

 of the reproductive cells. 



So'mite. One of the serial segments or meta- 

 meres of a metamcric animal. 



Spe'cies (L., appearance). Groups of actually 

 or potentially interbreeding natural popula- 

 tions that resemble one another closely and 

 which are reproductively isolated from other 

 such groups. 



Sperm (Gr., seed). A mature male reproduc- 

 tive cell or gamete. 



Sper'ma-ry (Gr. sperma, seed). The male re- 

 productive gland. 



Sper'ma-tid ( Gr. sperma, seed ) . A male germ 

 cell immediately before assuming the form 

 of a sperm. 



Sper'ma-to-gen"e-sis (Gr. sperma, seed; genesis, 

 origin). The process of formation of sperma- 

 tozoa. 



Sphinc'ter (Gr. sphinggein, to bind tightly). 

 A ring of smooth muscle surrounding a tube 

 or opening, which, by its contraction, closes 

 the lumen. 



Spic'ule (L. spiculum, a little point). One of 

 the many solid structures that comprise the 

 skeletal framework of a sponge. 



Spi'nal corumn (L. spina, thorn. L. columna, 

 column). A series of vertebrae in the verte- 

 brates, which encloses the spinal cord. 



Spi'nal cord (L. spina, thorn. Gr. corde, 

 string). Part of the central nervous system 

 extending the length of the spinal column 

 and continuing anteriorly into the brain of 

 vertebrates. 



Spin'dle (A.S. spinnan, to spin). A structure 

 formed in the cytoplasm during mitosis and 

 appearing to be made up of fibers arranged in 

 the form of a spmdle. 



Spin'ner-et (A.S. spinnan). Structures present 

 on the abdomen of spiders; fingerlike organs, 

 having tiny spinning tubes at their bases, from 

 which a fluid issues which hardens as it 

 comes in contact with air to form silk 

 threads. 



Spi'ra-cle (L. spiraculum, air hole). In insects, 

 an external opening of the tracheal or respir- 

 atory system; in the cartilaginous fishes, the 

 modified first gill slit. Also in tadpoles, the 

 atriopore. 



Splanch'nic (Gr. splanchnon, en trail). Per- 

 taining to the viscera. 



Spleen (Gr. splen, spleen). A large organ, 

 characteristic of most vertebrates, lying near 

 the stomach and known to destroy red blood 

 corpuscles in mammals. 



Spore (Gr. spora, seed). A special reproducfive 

 body of one of the lower organisms. It is usu- 



