GLOSSARY 441 



HORMONE. An internal secretion, usually from a ductless gland, 

 which is distributed by the blood and influences the activities 

 of one or more parts of the body. 



HYALINE. Pellucid or glassy. 



HYBRID. The progeny of parents which differ in regard to one or 

 more characters. 



HYDROIDS. A group of animals allied to Hydra, exhibiting alterna- 

 tion of generations. 



IMMUNITY. Resistance of the body to infection by disease-produc- 

 ing organisms. Exemption from disease. 



INFUNDIBULUM. A funnel-like outgrowth from the ventral wall of 

 the diencephalon. See Pituitary Body. 



INTERCELLULAR DIGESTION. Digestion by the secretion of enzymes 

 into a digestive cavity; e.g., in Earthworm and Man. See Intra- 

 cellular digestion. 



INTERNAL RECEPTORS. Sense organs within the body. See Exter- 

 nal receptors. 



INTERNAL SECRETION. See Hormone and Ductless Gland. 



INTESTINE. Portion of the alimentary canal from pyloric end of 

 stomach to anus. Divided into small and large intestine. 



INTRACELLULAR DIGESTION. Digestion of food within the cell it- 

 self; e.g., in Paramecium and to some extent in the endoderm 

 cells of Hydra. See Intercellular digestion. 



INTUSSUSCEPTION. Interstitial growth by the addition of new 

 particles throughout the whole mass of protoplasm. Contrasted 

 with growth by accretion, or the deposition of particles on the 

 surface as in crystals. 



INVAGINATION. Sinking or growing in of a portion of the surface of 

 a hollow body; e.g., during transformation of blastula to gastrula. 



INVERTEBRATE. An animal without a notochord or a vertebral column. 



IRRITABILITY. The power of responding to stimuli, exhibited by all 

 protoplasm. 



KARYOLYMPH. The more fluid material of the nucleus in contrast 

 with the linin and chromatin. 



KARYOSOME. An aggregation of part of the chromatin material 

 within the nucleus. A 'net-knot'. See Nucleolus. 



