404 PRISCIl'I.ES OF ANIMAL JilOLnaV 



Spermaducal pore (sper' ma tin' kai pore'). Ono of t lie t wo prominent openings 

 through which spermatozoa issue from the earthworm and simihxr animals. In 

 the common earthworm they are situated on the fifteenth metamerc. 



Spermary (xper' ma ri). See testis. 



Spermatheca {sper' ma the' ka). See seminal receptacle. 



Spermatid (sper'matid). One of the two cells formed by the second maturation 

 division of the male germ cells. By transformation in shape the spermatids be- 

 come mature spermatozoa. 



Spermatocyte {sper' ma to site). A male germ cell between the beginning of matura- 

 tion and the second maturation divison. A spermatocyte is called primary 

 during the growth period and jirior to the first maturation division; secondary 

 after the first division but prior to the second. 



Spermatogenesis {sper' ma to jen' e sis) . The maturation of male germ cells. 



Spermatogonium (sper' ma to go' ni rim) (pL, spermatogonia). One of the early 

 germ cells of a male animal, prior to the beginning of maturation. 



Spermatophore (sper' ma to fore). A mass of spermatozoa, sometimes resting upon 

 a stalk or being otherwise attached, as in some salamanders. 



Spermatozoon {sper' ma to zo' on) {pL, spermatozoa). The male germ cell in 

 animals. 



Spermophile {sper' mo file) . A common term applied to several of the ground- 

 squirrels and gophers. 



Sphenodon (sfen' o don) . A genus of reptiles of the order Rhynchocephalia. But one 



living species is known. 

 Spheroid {sfe' raid). Of nearly spherical shape. 

 Spicule {spik' ule). A body of various shapes commonly of calcareous or siliceous 



material, forming part of the skeleton of a sponge. 



Spinal cord (spi' nal kord'). That part of the central nervous system of vertebrate 

 animals lying behind the brain and largely enclosed in a channel in the vertebrae. 



Spindle {spin' d'l). A group of structures resembling threads, in the form of a spindle, 

 formed in the cytoplasm of a cell during mitosis. 



Spiracle {sjn' ra k'l). In frog tadpoles, an opening through which water passes 

 out of the gill chamber on one side. In insects, one of a number of openings on the 

 sides of the body through which air is introduced to the trachea*.. 



Spireme {spi' reem). The coiled or tangled thread formed by the chromatin network 

 of a cell prior to division. 



Splanchnic nerves {splank' nik). Three nerves from the thoracic sympathetic 

 ganglion. 



Splint (splint) . A bone at either side of the foot of the horse and some of its relatives, 

 being the remnant of a lost toe. 



Spongin (spun' jin). The horny material of the skeleton of the bath sponges. 



Spontaneous generation (spon ta' ne us jen' e ra' shun). Same as abiogenesis. 



Sporadic (sporad' ik). Occurring at irregular intervals, often without apparent 

 reason; said of migration of animals. 



Spore (spore). One of a great variety of reproductive cells usually having protective 

 coverings. Often the term is limited to asexual reproductive cells. The word is 

 often compounded with qualifying prefixes, or preceded by qualifying adjectives. 



Sporocyst (spo' ro si.nt). The bag-like individual into which the miracidium of the 

 liver fluke develops in a snail as host. 



