260 GLOSSARY 



Marginal lappets. Small flaps of tissue near the sense organs of Dis- 

 comedusae. 



Mastax. In rotifers, the very active muscular grinding part of the di- 

 gestive tract. 



Maxilla. One of the mouth appendages of arthropods. 



Medusa. Jelly fish; the sexual stage of certain coelenterates. 



Membranelles. Organelles formed of a double row of fused cilia found 

 in some cilates. 



Meropod. The second segment from the base of the endopod of a 

 crustacean. 



Mesenteric filament. In Actinozoa, the thickened free edge of certain 

 mesenteries. Gland cells and nettle cells are present here. 



Mesentery. A membrane which supports the intestine. In Actinozoa, 

 a membranous lamella or sheetlike portion having mesoglea for 

 its middle layer and covered on either face by endoderm. 



Mesoglea. The jelly-like substance which separates the ectoderm and 

 endoderm of a coelenterate. 



Metagenesis. In animals, alternation of generations. 



Metamere. One of the serial body segments of an animal, as in an- 

 nelids. 



Metamorphosis. In animals, a change in structure, as from larval to 

 adult stage. 



Metapleural fold. One of a pair of folds on the sides of Amphioxus. 



Micronucleus. In general, the smaller of the two nuclei in ciliates. 



Moniliform. Resembling a string of beads. 



Monoecious. Said of species in which the male and female gonads are 

 present in the same individual. 



Mouth. The opening through which food is taken. 



Myoneme. A contractile fiber, as in Vorticella. 



Nacre. The innermost layer of a mollusc shell. 



Nematocyst. The stinging organ contained in the cnidoblast. 



Nephridiopore. The external opening of a nephridium. 



Nephridium. Excretory tubule. 



Nephrostome. The opening from the coelom into a nephridium. 



Nerve connective. In invertebrates, a nerve connecting two ganglia 

 not of a pair. 



Nettle cell. Cnidoblast. 



Neuropodium. The ventral division of a parapodium of an annelid. 



Nidamental gland. In certain molluscs, an accessory reproductive 

 gland possessed by females. 



Notochord. A dorsal, living, internal, supporting structure characteris- 

 tic of Chordata. 



Notopodium. The dorsal division of a parapodium of an annelid. 



