GLOSSARY 57 



Metamorphosis: A change in body form as when the grub changes 

 into a butterfly. 



Metathorax: The posterior part of the thorax of insects, typically 

 bearing the posterior legs and the posterior pair of wings. 



Metazoa: Animals composed of many cells: animals in which 

 one or more tissues are present. 



Mouth parts: The different appendages grouped closely about 

 the mouth of arthropods which are used in capturing or 

 chewing food. 



Multinucleate: Having many nuclei within one cell wall. 



Nematocysts: The stinging bodies of Hydra and other coelen- 

 terates. 



Notochord: A cylindrical rod of cells beneath the nervous system. 

 It is the first stage in the development of the vertebral column 

 (backbone) of vertebrates; usually present only in embryos. 



Nymphs: Frequently used as synonymous with larvae, here 

 used to designate the young of insects with an incomplete 

 metamorphosis. 



Operculum: In snails, a chitinous structure borne on the foot 

 which closes the mouth of the shell when the foot is with- 

 drawn; in fishes, the covering of the gills. ' 



Ovaries: The female reproductive organs which originate the eggs 

 or ova. They can frequently be distinguished under the 

 microscope by the fact that they contain large egg cells. 



Palpi: Segmented antennal-like processes attached to the mouth 

 parts of some arthropods; also a shortening of pedipalpi, 

 the second pair of appendages in arachnids. 



Parapodia: Fleshy outgrowths from the body wall of some annelids 

 which bear setae. 



Parasite: An animal which lives in or on some other animal from 

 which it obtains its food. 



Parenchymatous: A loose spongy tissue like the pith of plants. 



