GLOSSARY 169 



gastro-vascular. The inner cavity of hydra, hydroids and 

 medusae which performs both digestive and circulatory 

 functions. 



genital. Pertaining to reproduction or the reproductive 

 organs. . 



germ layer. Any one of the three embryonic tissues, ecto- 

 derm, entoderm or mesoderm. 



giant fibers. A group of large tubes in the dorsal portion 

 of the nerve cord of annelids. They may represent 

 degenerated nerve fibers or supporting structures. 



gizzard. A muscular stomach in which food is crushed and 

 ground. 



gland. A part or organ for secreting some substance to be 

 used in, or eliminated from, the body. 



glottis. The opening from the mouth into the trachea. 



gonangium. A reproductive individual in some hydroids, 

 covered by an enlargement of the perisarc. 



granular. Composed of granules or small grains. 



II 



hermaphrodite. An animal containing both male and female 



sex organs. 

 histology. The science treating of the microscopic structure 



of animal and plant tissues, 

 homology. Similarity in structure and origin, 

 hydranth. One of the individual polyps of a hydroid colony, 

 hydroid. Resembling hydra ; marine, usually colonial animals 



of the phylum Ccelenterata. 

 hydrotheca. The vase-shaped expansion of the perisarc 



which covers and protects the hydranth of certain 



hydroids. 



