GLOSSARY 215 
Mantle: the integumental fold in mollusks which secretes the shell; mus- 
sel, 90; oyster, 100; clam, 104; snail, 113; squid, 124: the body-wall of 
ascidians beneath the tunic, 136. 
Manubrium : the projection of a medusa’s body which bears the mouth, 
167, 178, 175. 
Maxilla: the paired mouth-parts immediately behind the mandibles in 
arthropods; grasshopper, 13; beetle, 14; wasp, 14; caterpillar, 20; 
spider, 25; crayfish or lobster, 30; sow-bug, 47; amphipod, 49; cope- 
pod, 54; Daphnia, 56. 
Maxillipeds: the anterior thoracic appendages which assist in mastication 
in crustaceans; crayfish or lobster, 30; sow-bug, 47; amphipod, 49; 
Caprella, 50. 
Medusa: a medusoid which becomes a free-swimming jelly-fish, 163, 169, 
175. 
Medusoid: the sexual generation of a hydromedusan, 163, 169. 
Megalopa: a larval stage of the crab, 51. 
Mentum : a division of the labium in insects, 13. 
Mesentery: a lamella which supports some one of the viscera; Nereis, 64; 
Bugula, 86; squid, 127; starfish, 145; sea urchin, 152; sea cucumber, 
156; sea anemone, 179. 
Mesosternum : the ventral surface of the mesothorax in insects; wasp, 3; 
grasshopper, 10. 
Mesothorax: the second thoracic somite in insects; wasp, 2; grass- 
hopper, 10. 
Metamere: one of the serial, homologous body-segments, together with its 
appendages, which form the body of an articulate animal. 
Metamorphosis: the quiescent period in the life of a holometabolic insect 
during which it changes from a larva to an imago. 
Metasoma: the primitive segmented trunk of an articulate animal, 62, 68. 
Metasternum: the ventral surface of the metathorax in insects; wasp, 3; 
grasshopper, 10. 
Metastomium : the posterior portion of the prosoma of an annelid, 62, 69. 
Metathorax: the third thoracic somite in insects; wasp, 2; grasshopper, 9. 
Metazoa: the division of the animal kingdom comprising the many-celled 
animals, 191. 
Micronucleus: the smaller of the nuclear bodies in infusorians; Parame- 
cium, 186; Vorticella, 190. 
Mother-of-pearl: the inner layer of the shell of mollusks; mussel, 91; 
clam, 105. 
Moult : to shed the cuticula or the outer portion of it. 
