GLOSSARY 199 



Maxillipeds: the anterior thoracic appendages which assist in mastication 



in crustaceans: crayfish or lobster, 27; sow-bug, 41; amphipod, 43 ; 



Caprella, 44. 



Medusa: a medusoid which becomes a free-swimming jelly-fish, 149, 155. 

 Medusoid: the sexual generation of a hydromedusan, 149, 155. 

 Megalopa : a larval stage of the crab, 45. 

 Mentum: a division of the labium in insects, 11. 

 Mesentery: a lamella which supports some one of the viscera ; Nereis, 58 ; 



Bugula, 80 ; squid, 117 ; starfish, 135 ; sea urchin, 142. 

 Mesosternum : the ventral surface of the mesothorax in insects ; wasp, 3 ; 



grasshopper, 8. 



Mesothorax : the second thoracic somite in insects ; wasp, 2 ; grass- 

 hopper, 8. 

 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 an holometabolic insect 



during which it changes from a larva to an imago. 



Metasoma: the primitive segmented trunk of an articulate animal, 56, 62. 

 Metasternum : the ventral surface of the metathorax in insects; wasp, 3; 



grasshopper, 8. 



Metastomium : the posterior portion of the prosoma of an annelid, 56, 63. 

 Metathorax: the third thoracic somite in insects; wasp, 2; grasshopper, 8. 

 Metazoa : the division of the animal kingdom comprising the many-celled 



animals, 171. 

 Micronucleus : the smaller of the nuclear bodies in infusorians ; Parame- 



cium, 166; Vorticella, 170. 

 Mother-of-pearl : the inner layer of the shell of mollusks : mussel, 85 ; 



clam, 95. 



Moult : to shed the cuticula or the outer portion of it. 

 Mouth-parts: the masticatory appendages on the head of arthropods; wasp, 



2; grasshopper, 10; beetle, 11; wasp, 11; caterpillar, 18 ; centiped, 



20 ; crayfish or lobster, 24 ; crab, 37. 

 Mysis stage: a larval form of the lobster, 46. 



Nauplius : a larval form of crustaceans, 53. 



Nematocyst: the stinging organ in the Cnidaria which is within the cnido- 



blast; Hydra, 147; tubularian, 151; campanularian, 157. 

 Nephridium : a urinary tubule in annelids ; Nereis, 59 ; earthworm, 67. 

 Nephrostome : the ciliated opening of a nephridium into the body-cavity ; 



Nereis, 59 ; earthworm, 67. 



