510 APPENDIX 



Soma. Body tissue (somatoplasm) in contrast with germinal' tissue (germ 

 plasm) . 



Special Creation. Doctrine that each species was specially created. Im- 

 plies fixity of species. See Evolution. 



Species. In classification, the main subdivision of a genus. A group of 

 individuals which do not differ from one another in excess of the limits of 

 'individual diversity,' actual or assumed. 



Sperm. Male gamete. Spermatozoon. 



Spermatid. Male germ cells after the final maturation division but be- 

 fore assuming the typical form of the ripe sperm. 



Spermatocytes. Cells arising from the spermatogonia. Primary sperma- 

 tocyte arises by growth from the last generation of spermatogonia. 

 Primary divides to form two secondary spermatocytes. 



Spermatogenesis. The development of the sperm from a primordial 

 germ cell. 



Spindle. The fiber-like apparatus between the centrosomes during 

 mitosis. 



Spiracles. Openings on the body surface leading into the tracheal system 

 of Insects. 



Spleen. A vascular ductless organ of most Vertebrates, usually situated 

 near the stomach, that acts chiefly as a stabilizer of the supply of red 

 blood corpuscles. 



Spongin. A horny substance, chemically allied to silk, forming the fibers 

 of the skeleton of certain Sponges; e.g., the Bath Sponge. 



Spontaneous Generation. See Abiogenesis. 



Spore. A cell which gives rise without fertilization to a new individual. 

 Also the resistant phase assumed by certain unicellular organisms; e.g., 

 Bacteria, Sporozoa. 



Sporulation. Occurrence of several simultaneous divisions by which a 

 unicellular organism is resolved into many smaller cells. Formation of 

 spores. 



Statocysts. Organs of equilibrium; e.g., in medusae. 



Stimulus. Any condition which calls forth a response from living matter. 

 See Irritability. 



Symriosis. The association of two species in a practically obligatory and 

 mutually advantageous partnership; e.g., Lichens, Hydra (green). 



Sympathetic Nervous System. See Autonomic System. 



Synapse. The contact of one nerve cell with another, which makes pos- 

 sible the conduction of a nervous impulse from cell to cell. 



Synapsis. The pairing of homologous chromosomes during maturation 

 of the germ cells. 



Synaptic Mates. Homologous chromosomes of maternal and paternal 

 origin that pair during synapsis. 



