GLOSSARY 



265 



Siphon. One of the two tubes concerned with the passage of water 

 through a mollusc or a tunicate. Water enters through the in- 

 current siphon and flows out through the excurrent siphon. 



Siphonoglyph. The ciliated groove leading into the actinopharynx 

 from a corner of the mouth. 



Somite. Metamere; one of the serial body segments of an animal. 



Sperm. Spermatozoon; male reproductive cell. 



Spermary. A temporary sperm-producing organ; a testis. 



Spermatheca. A seminal receptacle, used for storing spermatozoa in 

 the female. 



Spermatophore. A specially formed packet of spermatozoa. 



Spermatozoon. Male reproductive cell. 



Sperm sphere. A mass of spermatozoa in the earthworm. 



Spicules. Minute skeletal bodies characteristic of sponges. 



Spinneret. One of the organs by means of which a spider spins its 

 thread. 



Spiracle. Breathing pore; external opening of the tracheal system. 



Spiral valve. The spirally wound internal fold of the wall of the in- 

 testine in elasmobranchs and certain other fishes. 



Spongin. The specialized spicule material of which the fibers of the 

 commercial sponges are composed. 



Spore. In animals, especially Protozoa, a cell, the product of multiple 

 fission, which is capable of developing into a new organism. 



Sporoblasts. In sporozoa, a cell which divides into sporozoites. 



Sporogony. Eeproduction by multiple fission (sporulation). Specifi- 

 cally, in Sporozoa, spore formation by a zygote after encystment. 



Sporont. The detached stage of Gregarina. 



Sporosac. In coelenterates, a sac which contains the generative cells— 

 an undeveloped, possibly degenerate medusa. 



Sporozoite. In Sporozoa, a small, usually elongate, sickle-shaped or 

 ameboid spore produced after zygote formation. 



Sporulation. The act of forming spores; multiple fission. 



Stalk. A stem or a peduncle. 



Statoblast. Asexual reproductive body of certain Bryozoa. 



Statocyst. An organ of equilibrium present in many invertebrates. 



Statolith. The body or bodies present within the cavity of a statocyst. 



Sternum. The ventral covering of a segment of an arthropod. 



Stigma. In insects, one of the external openings of the trachea; one 

 of the apertures in the pharynx of an ascidian. 



Stolon. An extension of the body wall from which buds are developed. 



Stomach. In invertebrates, the storage (food) division of the alimen- 

 tary canal. 

 Stomach-intestine. A division of the alimentary canal which functions 

 as both stomach and intestine, as in the earthworm. 



