542 The Ohio Naturalist. [Vol. VI, No. 8, 



properly called "nascent" organs. Thus the lung of a reptile 

 must- at one time have been a nascent lung while gills were used 

 to aerate the blood. The hypophysis of a moss is a nascent leaf 

 whether it ever develops any further or not. Such organs were 

 called "prophetic" by Agassiz in harmony with his theory of 

 creation. If a noun is to be used it appears to the writer that 

 "primordium" is the correct expression. Thus "primordial 

 organ" becomes synonymous with "nascent organ" and should 

 perhaps have the preference. 



Definition — Nascent organ (Lat. nasci, nascens) — An organ at 

 the beginning of its evolution or at the beginning of its develop- 

 ment in the race ; an organ in its first stages of evolution as com- 

 pared with other homologous organs. 



3. If an organ was developed in the past but is now contin- 

 ually imperfect or undeveloped in the individuals of a species it 

 is called a "vestigial" organ or a "vestige." The three small 

 sterile stamens in a Catalpa flower are vestigial. The splint 

 bones in a horse and the dew-claws on a cow's foot are examples 

 of vestigial organs. Such organs even if no longer functional 

 may still be useful. Some undeveloped organs may however not 

 be vestigial. The incepts may be present in the embryonic state 

 of the individual and may or may not develop, depending on 

 the sex determined during the development of the organism. 

 Such organs may in some cases be vestigial or they may only be 

 special cases of abortion. 



Definition — Vestigial organ, vestige (Lat. vestigium) — An 

 organ which was normally developed in the past history of the 

 race but which has become permanently reduced, never develop- 

 ing completely in any individual. 



4. If an organ normal in the species fails to develop properly 

 in an individual it may be called an abortive organ. A micro- 

 cephalic individual has an abortive head. A flower bud or a leaf 

 may be abortive by reason of an unfavorable position on the 

 stem. Abortive organs may sometimes be atavistic, the devel- 

 opment having stopped at a stage representing a more primitive 

 condition of the race. Abortive should not be used in the sense 

 of vestigial. 



Definition — Abortive organ (Lat. abortare.abortivus)— An or- 

 gan normal in the species but which has failed to reach full de- 

 velopment in the individual. 



5. Organs properly developed in the individual sometimes 

 become reduced through disease or other causes. Such organs 

 are properly called "atrophied" organs. 



Definition — Atrophied organ (Gr. atrophia) — An organ which 

 is normal in the species and fully developed in the individual, 

 but which has become reduced through pathological conditions 

 or through disuse. 



