GLOSSARY 



675 



Ho'mo-z/'gote (Gr. homos, same; zeugon, 

 yolk). An individual in which the members 

 of a given allelic pair of genes are alike, for 

 example, BB or bb. Compare with Heterozy- 

 gote. 



Hor'mone (Gr. hormon, from hormaein, to 

 arouse or excite). A chemical regulator or 

 coordinator secreted by cells or a ductless 

 gland and having a specific action on some 

 organ or organs at a distance from the gland. 

 It is carried by the blood or other body 

 fluids. 



Host (L. hostis, stranger). An organism that 

 provides food, shelter, or other benefits to 

 another organism. 



Hu'mer-us (L. humerus, shoulder). A bone of 

 the vertebrate upper arm. 



Hy'a-line (Gr. hyalos, clear). Glassy or semi- 

 transparent. Applied to the clear substance 

 of protoplasm. 



Hy'brid (L. hybrida, mongrel). An individual 

 resulting from the union of a sperm and egg 

 which differ in one or more genes; a heterozy- 

 gote. 



Hy'dranth (Gr. hydra, water serpent; anthos, 

 flower). The expanded end of a branch of 

 a hydroid colony that is specialized for 

 vegetative function. 



Hy'dro-caur'us (Gr. hydor, water; kaulos, 

 stalk). The main stalklike stem of a hydroid 

 colony. 



Hy'droid (Gr. hydra, water serpent; old, like). 

 Hydroid used as an adjective pertains to the 

 Hvdrozoa; used as a noun it refers to the 

 polyp form of a hvdrozoan, as distinguished 

 from the medusa form. 



Hy-drol'y-sis (Gr. hydor, water; lysis, loosing). 

 A process in which a complex compound is 

 digested into one or more simpler com- 

 pounds through a reaction with water. 



Hy'dro-rhi"za (Gr. hydor, water; rhiza, root). 

 The basal portion of a hydroid colony, often 

 branched and rootlike; used for attachment 

 to substratum. 



Hy'dro-the"ca (Gr. hydor, water; theke, cup). 

 The transparent membrane that extends 

 from the pcrisarc and surrounds the main 

 part of a hydranth. 



Hy'oid (Gr. hyoides, Y-shaped). A group of 

 bones and cartilages at or near the base of 

 the tongue. 



Hy'per-ton"ic (Gr. huper, beyond; tonikos, 



strength ) . In terms of a living cell, the con- 

 centration of water molecules is greater in- 

 side the cell than on the outside; therefore 

 more water molecules pass out of the cell 

 than into it. This results in the cell's shrink- 

 ing. 



Hy-poph'y-sis (Gr. hupo, under; physis, 

 growth ) . The pituitar}' gland in the inverte- 

 brate. See Pituitary and Infundibulum. 



Hy'po-stome (Gr. hupo, under; stoma, mouth). 

 The region surrounding the mouth in coelen- 

 terates. 



Hy-poth'e-sis (Gr., proposal). A tentative solu- 

 tion or explanation of a problem which has 

 not yet been proved to be either true or 

 false. 



Hy'po-ton"ic (Gr. hupo, under; tonikos, 

 strength). In terms of a living cell, the con- 

 centration of water molecules is greater on 

 the outside of the cell than inside; there- 

 fore more water molecules pass into than out 

 of the cell. This results in the cell swelling. 



I-den'ti-cal twins. Two individuals de\eloped 

 from a single fertilized egg and, therefore, 

 having identical sets of genes. Also called 

 monozygotic or one-egg twins. 



Il'e-um (L., grain). The posterior and longest 

 part of the small intestine of a mammal. 



In"breed'ing (L. in, in; M.E. breden). The 

 crossing or mating of closely related individ- 

 uals, such as first cousins, or brother and 

 sister. 



In-fun-dib'u-lum (L. infwidibulum, funnel). 

 A stalklike down-pushing of the dienccpha- 

 lon of the brain, which, along with the em- 

 bryonic hypophysis, will give rise to the 

 pituitary gland of the adult. 



In-gest' ( L. ingestiis, from ingerere, to put in ) , 

 To take any substance from the outside, 

 especially food, into the digestive tract of 

 an animal. 



In-scr'tion (L. insertus, from inserere, to con- 

 nect, insert). The place of attachment of a 

 muscle to a moxable part, in contrast to 

 the origin which is the point of attachment 

 to a relatively immovable part. 



In'su-lin (L. insula, island). Hormone secreted 

 b\ the islets of Langcrhans of the pancreas. 



In-tcg'u-ment (L. integumentum, covering). 

 The outer covering, especially the skin, of 

 a vertebrate. 



