GLOSSARY 241 



SOMATIC PLASM. Protoplasm of the body organs and tissues as opposed to 

 the reproductive or germinal plasm. 



SOMATOBLAST. A particular cell in early development destined to give 

 rise to the ventral plate of the embryo. 



SORUS. One of the aggregates of spore cases on the fronds of ferns. 



SPERMATOGENESIS. The development of spermatozoa from the primitive 

 or primordial sex cells. 



SPERMATOPHORE. A special capsule, case or sheath containing spermatozoa. 



SPIRACLE. An aperture for admitting air. 



SPIREMB. A coiled mass of chromatin in thread form at the beginning of 

 nuclear division. 



SPORANGIUM. The case or sac within which spores are produced. 



STEREOME. The elements which impart strength to fibrovascular bundles 

 and other tissues of plants. 



STIMULUS. Anything acting on living matter which calls forth a response. 



STOMA. Mouth; a breathing pore in plant leaves. 



STOMODAEUM. The anterior part of the digestive tract formed by ingrowth of 

 ectoderm. 



SYMBIOSIS. Obligatory living together of two organisms for mutual benefit. 



SYNAPSIS. The union of maternal and paternal chromosomes prior to 

 the maturation divisions. 



TAXONOMY. The science of classification. 



TETRAD. Bivalent chromosomes which ' appear to be 4-parted in the 

 maturation divisions. 



TISSUE. An aggregate of similar cells or cell products having the same 

 function. 



TOXIN. A poison; usually employed to indicate products of protein break- 

 down during the metabolic processes. 



TRACHEA. As used here, the air-holding tubes of insects and allied forms. 



TRICHOCYST. One of the minute hair-like bodies developed in the cortical 

 protoplasm of an infusorian. 



TRYPSIN. A proteolytic ferment capable of rapidly digesting albumins. 



TYPHLOSOLE. A fold of the intestine of certain annelids and other inverte- 

 brates, formed by the inturning of the wall of the intestine along the 

 dorso-median line and projecting into the intestinal cavity. 



UREA. The final product of protein decomposition in the body, forming 

 the chief solid constituent of the excretory fluid of many animals. 



XANTHOPHYLL. A yellow-green substance derived from chlorophyll. 



ZOOGLOEA. A mass of bacteria embedded in jelly of their own secretion. 



ZYMASE. The enzyme of yeast which causes the breaking up of sugar into 

 alcohol and carbon dioxide, or alcoholic fermentation. 



ZYMOGEN. Substance from which enzymes are formed by internal changes. 



