404 BIOLOGY 



humor. A name applied to the transparent liquids in the eye, 197. 



HUXLEY. 40. 



hybrids. Organisms resulting from the crossing of different species, 268. 



Hydatina, 57, 247. 



Hydra, description of, 140. 



hydrocarbons, 9. 



hydroids. Animals closely related to Hydra, 148, 277. 



hydrophyte (Gr. hydor = water + phyton = plant). Plants living in 



water or in a very wet habitat, 

 hyoid. A V-shaped arch of bone under the jaw and surrounding the larynx, 



181. 

 hyomandibular. A chain of bones attaching the lower jaw to the skull 



hi the frog. 



hypha. One of the filaments of a mycelium, 

 hypoblast. Applied to the endodermal layer in the embryo, 

 hypophysis (Gr. hypo = under + phuein = nature). See pituitary body, 



193. 



ileum. A name given to the intestine below the duodeum. 

 ilium, 182. 



imago. The adult stage of an insect with a metamorphosis, 289. 

 imbibition (Lat. imbibire = to imbibe). The action of absorbing water, 



shown by many organic substances, 

 immutability of species (Lat. in = not + mutabilis = changing). The 



theory that species remain constant, 349. 

 imperfect flowers. Flowers in which either stamens or pistils are lacking, 



120, 121. 

 impregnation (Lat. impregnare = to make pregnant). See fertilization, 



257. 

 inbreeding. Breeding from a male and female of the same parentage, like 



brother and sister, 268. 

 income, of an animal, 219; of a plant, 220. 

 incubation (Lat. incubare = to he on). To keep warm. 

 Indirect development, 290. 

 individual, 67. 



individual variations, 337, 358. 

 indusium (Lat. induere = to put on). A covering over the sporangia in 



the sorus of a fern, 269. 

 inferior vena cava. The large venous trunk bringing the blood from the 



lower parts of the body to the heart: same as posterior vena cava, 190. 

 infundibulum. Any funnel-shaped or dilated organ, 193. 

 infusion. A preparation made by steeping a substance like hay in warm 



water. 



