June, 1906.] Terminology of Organs. 543 



6. Imperfectly developed or reduced organs of all types 

 may be called rudimentary organs or rudiments. So long then 

 as the nature of any incomplete organ is unknown, or speaking 

 generally, it may be called a rudimentary organ ; but with complete 

 knowledge, and speaking specifically, it will be called an incipient, 

 a nascent, a vestigial, an abortive, or an atrophied organ as the 

 case may be. 



Definition — Rudimentary organ , rudiment (Lat. rudimentum) 

 — An organ in the initial, incipient, or incomplete stage of develop- 

 ment; or one that has become reduced either in the history of 

 the race or of the individual. 



There are still other types or conditions of organs which may 

 be defined in a definite sense : 



1. Atavistic organs are such as show in the individual a re- 

 turn to some ancestral type. 



2. Retrogressive organs are such as are passing from a 

 higher to a lower or less perfectly developed condition or state of 

 organization. 



3. Abnormal organs are those which deviate from the usual 

 type in some extraordinary way, as in shape, size, number of 

 parts, color or other character. Good examples of abnormal 

 organs are shown in the following: a fasciated stem, a three-parted 

 Fuchsia, or a "web-toed" man. Abnormalities are frequently 

 inherited. 



4. Under the term malformed organs, may be included such 

 types as unusual growths due directly to some external condition 

 in the life of the individual, as an insect bud-gall, or a leaf blade 

 of a rhubarb grown in the dark. A good example is a pointed 

 leaf which has become emarginate through some accident dur- 

 ing its development. A malformation cannot be transmitted 

 unless acquired characters so called are inheritable. 



5. Transformed organs are such as show a change in the in- 

 dividual or the race from one type of structure or function to an- 

 other. A stamen developing into a petal is a transformed organ. 

 In such transformations there is a failure of the usual hereditary 

 tendencies to assert themselves while other tendencies present 

 in the same cells become dominant when they should be sup- 

 pressed. Insect wings are probably transformed gills and rep- 

 tilian lungs transformed air-bladders. 



6. Under the term "juvenile organs" may be included all 

 organs which appear on the young individual but which are ab- 

 sent in the adult. They may be special organs of the embryo, 

 or normally developed organs which later drop off or are absorbed. 

 The compound leaves of certain seedling Acacias which in the 

 adult stage have only phyllodes are good examples of juvenile 

 organs; the tail of a tadpole is a juvenile organ. The term em- 

 bryonic organ may be used for the earlier stage whenever there 



