GLOSSARY 501 



Hermaphrodite. An organism bearing both male and female reproduc- 

 tive organs; e.g., Earthworm. 



Heterozygous. Hybrid. Formed by gametes dissimilar in regard to a 

 given character, or characters, and producing gametes dissimilar in 

 regard to the character, or characters, in question. See Homozy- 

 gous. 



Histology. The science which treats of animal and plant tissues. Mi- 

 croscopic anatomy. 



Holozoic. Type of nutrition involving the ingestion of solid food. Char- 

 acteristic of animals. See Autotrophic and Saprophytic. 



Homologous Chromosomes. The members of a pair of chromosomes, of 

 a diploid group, one paternal and the other maternal in origin, which 

 bear homologous genes. See Synaptic Mates. 



Homologous Genes. Genes similarly situated on homologous chromo- 

 somes, and contributing to the same or different expressions of a char- 

 acter. Allelomorphs. Alleles. 



Homology. Fundamental structural similarity, regardless of function, 

 due to descent from a common form; e.g., wing of Bird and fore leg 

 of Dog. 



Homothermal. Animals provided with a mechanism which maintains 

 the body at a practically constant temperature, usually higher than 

 that of the environment; e.g., the 'warm-blooded' animals, or Birds 

 and Mammals. 



Homozygous. Pure. Formed by gametes the same in regard to a given 

 character, or characters, and producing gametes all the same in regard 

 to the character, or characters, in question. See Heterozygous. 



Hormone. An internal secretion usually from a ductless gland. Secreted 

 directly into the blood which distributes it throughout the body where 

 it selectively influences tissues and organs. 



Host. An organism in or on which a parasite subsists. 



Hyaloplasm. The clear ground-substance of protoplasm. 



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

 characters. A heterozygote. 



Hydranth. A feeding polyp of a Hydroid colony; e.g., Obelia. 



Hydroids. A group of animals (Coelenterates) exhibiting alternation of 

 generations; e.g., Obelia. 



Hydrolysis. Decomposition of a chemical compound by reaction with 

 water; e.g., in digestion. 



Hydrostatic Organ. Organ for regulating the specific gravity of an 

 animal in relation to that of water; e.g., the air-bladder of certain 

 Fishes. 



Hydrotheca. Vase-like expansion of the exoskeleton, or perisarc, about 

 a hydranth; e.g., of Obelia. 



