Glossary 



381 



centered can be said to have 

 been solved. 



EPIMORPHOSIS. The mode of re- 

 generation of organisms in 

 which a multiplication of cells 

 on the surface of injury is first 

 produced, then from this "em- 

 bryonal tissue," the new organ 

 or part is formed; contrasting 

 with morphalaxis, a mode of 

 new formation which consists in 

 a direct transformation of an 

 already existing part into the 

 new part. 



FACTOR (in Genetics). A hypo- 

 thetical unit of structure or of 

 chemical composition, contained 

 in the germ-cell, which in some 

 way is held to condition the de- 

 velopment of a particular char- 

 acter in the adult, or of a com- 

 plex of characters which are 

 transmitted in constant associa- 

 tion with one another. Factors 

 are believed to interact with one 

 another in development, and at 

 times to be so "linked" that they 

 are only partially independent in 

 transmission. 



FLAGELLUM. A lash-like appen- 

 dage or large cilium serving as 

 an organ of locomotion in some 

 Protozoa and some bacteria. 



FORAMINIFERA. A class of rhizo- 

 podous marine Protozoans, usu- 

 ally having a porous shell. 



FORMATIVE STUFFS. Hypothetical 

 substances which are supposed 

 to be formed in one part of an 

 organism and transported to an- 

 other part, there to produce, or 

 to influence the production of 

 new organs. For example, sev- 

 eral botanists have supposed that 

 the flower substance of some 

 plants is actually produced in 

 the leaves. 



GAMETE. A reproductive cell 

 which unites with another repro- 

 ductive cell to form a zygote. 



GASTRULA. That stage of embry- 

 onic development in many ani- 



mals which consists of two germ- 

 layers inclosing a central cavity. 

 It* is produced from the blastula 

 (which see) by the in-sinking of 

 one-half of this into the other. 



GEMMIPAROUS. Producing gemma?, 

 or buds (reproducing by bud- 

 ding), applicable to both plants 

 and many animals. 



GEMMULE. 'in the original and 

 proper sense a small aggregation 

 of cells set apart in the tissues 

 of some plants and animals, 

 notably in many sponges, for the 

 purpose of reproduction. In ori- 

 gin and structure gemmules are 

 more like buds than eggs, 

 though the end served is very 

 similar to that served by seeds. 

 In a secondary and wholly hypo- 

 thetical sense, gemmules are 

 imaginary, minute bodies given 

 off by all the tissue cells of an 

 organism and assembled in the 

 germ cells, there to cause the 

 development of the next genera- 

 tion. This taking of a very con- 

 crete name from botany and 

 zoology, and using it in a wholly 

 imaginary way to explain hered- 

 itary development was due orig- 

 inally to Charles Darwin, but 

 with more or less unimportant 

 variations of meaning has since 

 been resorted to by many of the 

 best known biologists. 

 This example indicates the great 

 importance for biology, espe- 

 cially for the biology of repro- 

 duction and development, of dis- 

 tinguishing between the same 

 terms used in a strictly objective 

 and descriptive sense on the one 

 hand, and in hypothetical, or 

 purely imaginary sense on the 

 other. 



GENE. A term much used in pres- 

 ent-day genetical science, but ap- 

 parently not differing in any sig- 

 nificant particular from factor 

 (which see). 



GENETIC. Pertaining to genetics, 



