120 NATURAL HISTORY 



Gastrovascular — serving both digestive and circulatory purposes. 



Germ cell — sex cell. 



Gill cleft — a branchial opening formed on the side of the pharynx. 



Gill filaments — the soft filamentous structures on the respiratory organs (gills) 

 of aquatic animals. 



Gland — an organ which secretes material to be used in, or excreted from, the 



body. 

 Halteres — a pair of small capitate bodies representing rudimentary wings in 



flies, used as balancers. 



Haploid — having the number of chromosomes characteristic of mature germ- 

 cells for the organism in question. 



Hemocoele — an expanded portion of the blood system which takes the place of 

 a true coelom. 



Hepatic caecum — blind pouch or diverticulum of or in region of liver. 



Hermaphroditic — pertaining to an organism with both male and female repro- 

 ductive organs. 



Heterocercal — having vertebral column terminating in upper lobe of fin, which 

 is usually larger than the lower. 



Homocercal — with equal or nearly equal lobes, and axis ending near middle of 

 base. 



Hypha — one of the filaments composing the mycelium of a fungus. 



Incisors — front chisel-like teeth of either jaw. 



Incubate — ■ to keep warm and under other favorable conditions for hatching. 



Indirect development — undergoing metamorphosis, i.e., showing a decided change 

 in form and appearance from time of hatching until maturity. 



Integument — a covering or protective layer; skin. 



Keel — ridgelike process. 



Lamellae — thin platelike structures. 



Larvae — young stages in the development of some forms of animals, which be- 

 come self-sustaining but which do not have the characteristics marking adults. 



Lateral line — longitudinal line at each side of body of certain aquatic animals 

 marking position of sensory cells. 



Laterally compressed — narrow from side to side. 



Ligament — a band of connective tissue binding one bone to another. 



Lobate — divided into lobes. 



Lophophore — ridge bearing tentacles. 



Lung-books — respiratory organs formed like a purse with numerous compart- 

 ments or a book with edges of leaves exposed. 



Mammary glands — milk-secreting glands. 



Mantle — the soft outer fold of skin in molluscs which secretes the outer shell. 



Medusoid — like a jellyfish or medusa. 



Megasporangium — a macrospore-producing sporangium in plants. 



Megaspore — larger spore of heterosporous plants, regarded as female; embryo- 

 sac cell of seed plant. 



Membranous — resembling or consisting of a membrane ; pliable and semi- 

 transparent. 



Mesenchymatous — pertaining to mass of tissue intermediate between ectoderm 



and endoderm, derived from mesoderm. 

 Mesenteries — peritoneal folds serving as a bridge for blood vessels and for 



holding organs to body wall. 

 Mesoderm — the middle layer of tissue in a young animal embryo. 



