GLOSSARY 399 



Sciuridae (si u' ri dee). The family of rodents including the flying squirrels, squirrels, 



marmots, and chipmunks. 

 Sciurinae (si' u ri' nee). The subfamily of Sciuridae comprising the marmots, 



squirrels, and cliipmunks. 

 Sciuromorpha (si' u ro mor' fa). The suborder of rodents comprising the squirrellike 



forms. 

 Sciurus (si u' rus). The genus including the arboreal squirrels. 

 Scolex. The enlarged attaching organ from which are budded off the proglottides 



of a tapeworm chain. 

 Scyphozoa (si' fo zo' a). A class of Coelenterata, jellyfishes of large size which have 



no hydroid form in the Ufa cycle. 

 Secondary. For application to spermatocytes, see spermatocyte. For application 



to oocytes, see oocyte. 

 Secretin (se kre' tin). A substance produced in the small intestine and serving to 



stimulate secretion by the pancreas and liver. 

 Secretion. The act of producing from the blood or other fluids or substances in the 



protoplasm some new material to be used in metabolism or otherwise. Also the 



new substance thus formed. 

 Segmentation. Same as cleavage. 

 Self-fertilize. To fertilize the eggs of an individual by spermatozoa of the same 



individual. 

 Semicircular canal. One of several curved tubes forming part of the inner division 



of the ear in vertebrates. 

 Seminal receptacle. An organ in a female animal for the reception and storage of 



spermatozoa from the male. 

 Seminal vesicle. One of several bodies closely connected with the testes in the earth- 

 worm, in which a large part of the development of the spermatozoa takes place. 



Also, an enlargement in the vas deferens or similar duct in which spermatozoa 



may be stored in various animals. 

 Semipermeable membrane. A membrane which allows some substances to pass 



through it, but retards or excludes others. 

 Sensory. Pertaining to sensation; applied to a neuron which transmits an impulse 



resulting in sensation, or by extension to any other receiving neuron whether 



concerned with sensation or not. 

 Septum. A partition. 



Series. The rocks, collectively, which belong to a geological epoch. 

 Serum. The yellowish fluid which escapes from a blood clot; it is approximately 



the plasma without any fibrinogen. 

 Sessile. Attached directly, as distinguished from stalked. Sometimes, also, 



attached, as distinguished from free-Uving. 

 Seta (pi. setae, se' tee). A spine; specifically, one of the spines projecting from the 



somites of an earthworm and used for locomotion. 

 Sex-linked. Associated with sex; said of hereditary characters the genes for which 



are in the X chromosomes associated with sex. 

 Sexual. Involving the production of true germ cells, or the fusion of nuclei; said 



of reproduction, or of an individual employing such a mode of reproduction. 

 Shoal. A shallow place in a body of water; also a sandbank or bar which makes the 



water shallow. 

 Silurian. Of middle Paleozoic time, between Ordovician and Devonian. 

 Sinus node. A mass of rather undifferentiated tissue in the right auricle of the heart 



which receives stimuU and initiates the heart beat. 



