318 ANIMAL LIFE 
Sperm cell: 20. 
Spir'acle: one of the breathing openings of an insect situated on the 
side of the abdomen or thorax. 
Spon’gin : 20. 
Stimulus (pl. stimuli): that which excites action in plant or animal 
tissue. 
Stra'ta: layers, usually said of rocks, 
Stridula tion: 122. 
Sub-species: 151. 
Symbid'sis: 90. 
Tactile: referring to the sense of touch. 118, 
Tadpole : 58. 
Tén'tacle: a protruding flexible process or appendage, usually of the 
head of invertebrate animals, being used as an organ of touch, 
prehension, or motion. 
Térmitdphiilous: said of insects inhabiting the nests of termites. 
Vac'uole: a minute cavity containing air, water, or a chemical secre- 
tion of the protoplasm, found in an organ, tissue, or cell. 
Vestig'ial : 82. 
Vis'cera: the organs in the great cavities of the body, commonly used 
for the organs in the abdominal cavity. 
Voll (yok): 48, 
Zoé'a: 59. 
Zoogedg'raphy : 147. 
Z6'oid: one of the more or less independent members of a colonial or 
compound organism. 
Zool ogist: a student of animals, 
