34 2 Glossary 



Pro-to-zo'-a. The simplest animals, usually consisting of a single cell. 



Py-lo'-rus. The narrow opening between stomach and intestine. 



Recessive character. An inherited character which remains undeveloped 

 when mated with a dominant character. 



Reduction-Division. That maturation division in which the number of 

 chromosomes is halved. 



Reflexes. Relatively simple, automatic responses. 



Response. Any activity of an organism called forth by a stimulus. 



Reversions. The sudden reappearance of long-lost racial characters. 



Segregation. The separation of contrasting parental characters in the 

 offspring of hybrids, or of contrasting genes (allelomorphs) in the 

 formation of gametes. 



Self Differentiation. Differentiation due chiefly to intrinsic causes. 



Sensitivity. Capacity of receiving and responding to stimuli. 



Sex Chro'-mo-some. The "odd" or accessory chromosome which is sup- 

 posed to determine sex. 



Sex-limited. Any character which is found in one sex only. 



Sex-linked. Any character, the determiner of which is associated with 

 the determiner of sex. 



Simplex Factors or Character. A condition where the determiner for 

 a character is derived from one parent only. 



Sin'-is-tral snail. A type of snail in which the shell coils from base to 

 apex in an anti-clockwise direction. 



So'-ma. The body as contrasted with the germ cells. 



So-mat'-ic. Pertaining to the body, as contrasted with "germinal" pertain- 

 ing to the germ cells. 



So'-ma-to-plasm. The body-plasm as contrasted with the germ-plasm. 



So'-mite. A segment of the body of a segmented animal. 



Sper-ma'-to-cytes. The mother and grandmother cells of spermatozoa. 



Sper-ma-to-gen'-e-sis. The development of a spermatozoon from a prim- 

 itive sex cell. 



Sper-ma-to-go'-ni-a. Primordial sperm cells. 



Sper-ma-to-zo'-on. The mature male sex cell. 



Spindle. The nuclear division figure. 



Spi'-reme. A coiled thread of chromatin which appears in the nucleus at 

 the beginning of mitosis. 



Spi-ril'-la. A spiral type of bacteria. 



Sten'-tor. A ciliated protozoan. 



Ster-e-o-i'-so-meres. Molecules having the same composition but differ- 

 ent properties dependent upon varying spatial relations of their con- 

 stituent atoms. 



Stim'-u-lus. Anything acting on an organism which calls forth a response. 



