418 BIOLOGY 



sclerotic coat (Gr. scleros = hard). The outer covering of the eyeball, 196. 



sea nettles. See jelly fishes. 



sebaceous glands (Lat. sebum = fat). Oil glands in the skin. 



secreting cells. Cells which extract material from the blood and secrete 



special substances, 145, 161. 

 secretions. Materials eliminated by the glands and used by the body 



for some special purpose, e. g., gastric juice. 

 seed. A young plant surrounded by a shell and lying dormant; developed 



in higher plants only, for the purpose of distribution, 122. 

 seedling. The young plant in a seed, or just sprouting from a seed, 123. 

 segmentation. A term describing the division of the earthworm into 



segments, 155; the division of the egg into many cells in development 



(cleavage), 280. 



segment. The name applied to the rings of which a body like the earth- 

 worm is composed; metameres, 155. 

 segregation (Lat. segregare = to separate). The grouping together of 



individuals which show resemblances. 

 semicircular canals. Canals in the inner ear, associated with the sense 



of equilibrium, 198. 

 semilunar valves. Valves at the beginning of the pulmonary arteries and 



the aorta, 310. 



seminal receptacles. Sacs of the earthworm for holding the sperms re- 

 ceived at copulation, 165. 

 seminal vesicles. Sacs in the earthworm for holding sperms before they 



are ejected during copulation, 164, 200. 

 sensation. A conscious feeling, produced in the brain as the result of 



impulses reaching it from the various sense organs, 212, 316. 

 sensations in plants, 137. 

 sense organs. Organs at the outer ends of the nerves which are excited 



by external stimulation, 167, 172, 195, 212. 

 sensitiveness. Same as irritability, 219. 

 sensitive plants. Plants which respond quickly to touch by closing their 



leaves, 137. 



sepals. The 'leaves which form the calyx, 119. 



septa. Partitions separating chambers, especially in the earthworm, 157. 

 serous. Applied to glands secreting a thin, watery liquid, 

 serous membranes. Membranes lining the body cavity and thorax, 

 serum. The liquid part of the blood after the clot has separated, 

 setae. Minute bristles serving to aid the earthworm in locomotion, 167. 

 sexual reproduction. Reproduction by union of eggs and sperms, 71, 



238, 240, 262; distribution of, 266. In earthworm, 163; in frog, 214; 



in Hydra, 151; in plants; origin of, 263; purpose of, 335. 



