Online Dictionary of Invertebrate Zoology: Complete Work - Best Text

590Maggenti and Gardnerthe lateral cords, extending posteriorly and becoming trifurcateat the base of the lateral rays; possibly functioningto extend the bursa.musculus costerum lateralium internis (NEMATA: Secernentea)Bursa muscle that arises as paired submedianmuscles at the body wall anterior to the intestino-rectalvalve; each laterally extended branch entering the root ofthe lateral ray; possibly functioning to bend the bursa inwards.mushroom bodies (ARTHRO: Insecta) The two stalked nervestructures of the protocerebrum, that are connected withthe optic lobes. see corpora pedunculata.mushroom gland (ARTHRO: Insecta) Large mushroom-shapedseminal vesicles.mutafacient n. [L. mutatus, change; facere, to make] Gene orgenetic element that causes or increases the chance ofmutation at another site.mutagen n. [L. mutare, to change; Gr. gennaein, to produce]Any physical or chemical agent that increases mutationalevents.mutant n. [L. mutare, to change] An organism that undergoesmutation.mutation n. [L. mutare, to change] A structural change in agene, consisting of a replacement, duplication, or deletionof one or several pairs in the DNA.mutation frequency The frequency of mutants in a population.mutationism see De Vriesianismmutation rate Frequency with which a mutation occurs persite per generation.mutation theory A theory of the origin of new characteristicsin organisms as a result of changes in the genes. see saltation.mutator genes Any gene that causes an increase in mutationrates in other genes. see mutafacient.mutein n. [L. mutatus, change; Eng. protein] A mutationallyaltered protein analogous to the normal type.