386 PRINCIPLES OF ANIMAL BIOLOGY 



Interphase. The stage in the cycle of a cell in which it is not dividing: the so-called 

 "resting" stage. 



Interstitial cells. The cells of a testis which lie between the seminiferous tubules. 



Intracellular. Within a cell. 



Invagination. The folding of a layer of cells inward into a cavity. 



Ion. An atom or group of atoms bearing an electric charge. 



Ischium {is' ki um) {pi., ischia). The posterior of two ventrally located bones of the 

 pelvic girdle of vertebrate animals above "the fishes. 



Islands of Langerhans. Groups of isolated cells in the pancreas, which produce 

 insulin. 



Isogamete {i' so gam' eet). One of two gametes of equal size which fuse in reproduc- 

 tion. 



Isogamy {i sog' a mi). Fusion of like gametes in reproduction. 



Isolation. In evolution, the inability of species to cross with one another. 



Jejunum. The second of three divisions of the small intestine. 



Jensen, Zacharias. Dutch inventor of the microscope about 1591. 



Jugular vein. A large vein returning blood from the head. 



Jurassic. Of middle Mesozoic age; named from rocks in the Jura mountains. 



Karyokinesis {ka' ri o ki ne' sis). Same as mitosis. 



Kidney. The chief organ for the excretion of nitrogenous wastes in most vertebrates. 



Also an excretory organ in certain other animals. 

 Kinostemidae {ki' no stcr' ni dee). A family of turtles. 



Labial palp. One of two pairs of flattened organs beside the mouth of mussels. 



Labyrinth. The inner ear of vertebrates. 



Lacteal (lak' tc al). One of the minute vessels leading from the intestine to the 



• lymph ducts. 

 Lactose. Milk sugar, a disaccharide found in the milk of mammals. 

 Lacuna. A space in the matrix of bone which contains in life a bone cell. 

 Lamarck, de, Jean Baptiste, etc. Celebrated French naturalist and proponent of 



evolution, 1744-1829. 

 Lamella. A layer. 



Lamprey. An eellike animal of the class Cyclostomata. 

 Lampsilis {lamp' si lis). A genus of fresh-water mussels. 

 Large intestine. The enlarged portion of the digestive tract following the small 



intestine. 

 Larva. A free-living developmental stage of an animal in which certain adult 



organs are still lacking or in which organs are present that are lacking in the 



adult. 

 Lateral fold. One of two ridges of skin along the back of certain species of frogs, 



extending lengthwise at either side. 

 Lecithin {Ics' i thin). One of a number of lipoid substances common in egg yolk, 



nerve tissue, and other kinds of cells. 

 Leeuwenhoek, van, Anton {lay' ven hook). Dutch naturalist and microscopist, 1632- 



1723. 

 Leiolopisma {li' o lo piz' ma). A genus of skinks (lizards). 

 Lemming. A rodent of the family Muridae, to which the rats, mice, and muskrats 



belong. 

 Lepas anatifera {le' pas an' a tif cr a). A species of barnacle (subclass Cirripedia 



of the Crustacea). The goose barnacle. 



