170 GENERAL BIOLOGY 



I 



incurrent. A pore or tube through which water enters an 

 animal. 



infusoria. Protozoa found in infusions of organic matter; 

 ciliate protozoa. 



interstitial cells. Cells of hydra which fill the spaces be- 

 tween the bases of the ectodermal cells. 



irritability. Susceptibility of protoplasm to the influence 

 of stimuli. 



labium. One of the mouth parts of insects, the lower lip or 

 second maxilla. 



labrum. One of the mouth parts of insects, the upper lip. 



lamella. A thin plate or layer. 



larva. The free living young of an animal in which develop- 

 ment is accompanied by a metamorphosis. 



lateral. On or toward the side. 



ligament. A tough band which connects one part to an- 

 other; in the clam the elastic band which unites the 

 valves of the shell. 



M 



macronucleus. The larger of the two nuclei present in 



ciliated protozoa. 



mandible. The hard jaw of arthropods, one of a pair, 

 mantle. The fold of skin covering the body and secreting 



the shell in molluscs, 

 manubrium. The proboscis or sac-like stomach of the 



medusa, 

 matrix. The intercellular ground substance which separates 



the cells in such tissues as cartilage. 



