318 ANIMAL LIFE 



Sperm cell : 20. 



Spiracle : one of the breathing openings of an insect situated on the 



side of the abdomen or thorax. 

 Spon'gin: 20. 

 Stimulus (pi. stimuli) : that which excites action in plant or animal 



tissue. 



Stra'ta : layers, usually said of rocks. 

 Stridula tion : 122. 

 Sub-species : 151. 

 Symbiosis: 90. 



Tactile : referring to the sense of touch. 118. 



Tadpole: 58. 



Ten tacle : a protruding flexible process or appendage, usually of the 



head of invertebrate animals, being used as an organ of touch, 



prehension, or motion. 

 TermitSph ilous : said of insects inhabiting the nests of termites. 



VSc'uole : a minute cavity containing air, water, or a chemical secre- 

 tion of the protoplasm, found in an organ, tissue, or cell. 



Vestigial : 82. 



Vis'cera : the organs in the great cavities of the body, commonly used 

 for the organs in the abdominal cavity. 



Yolk (yok) : 48. 



Zoe a : 59. 



Z6oge8g'raphy : 147. 



Zo'oid : one of the more or less independent members of a colonial or 



compound organism. 

 Zoologist : a student of animals. 



