246 The Unity of the Orgamsm 



ency. There are many transitory structures among multi- 

 cellular organisms notably connected with reproduction, for 

 example the liectocotylized arms of some cephalopods, which 

 we never hesitate to call organs. And taking the animal 

 kingdom as a whole, think of the innumerable organs occur- 

 ring in the embryonal and larval lives of animals ; for in- 

 stance the placenta in mammals and the gills of frogs in 

 the tadpole stage. No one hesitates to call these "organs" 

 because they are transient. As long as this is so, we can- 

 not consistently let the transitoriness of cell parts stand in 

 the way of calling them organs. 



"The cilia and the stalk (of Vorticella) are definite, per- 

 manent organs, the first of the kind we have met with." ^^ 

 One can justify the use of the term organ as applied to 

 the Protozoan by quoting indefinitely from practical writ- 

 ings by the best authorities. Yet when we come upon defini- 

 tions of "organ" framed to meet the needs of cellular ele- 

 mentalism, we find that the practice above referred to would 

 be illegitimate. Some of these definitions are wonderfully 

 naive. Take this from the H andworterhiich der Naturwis- 

 seTischaften,undcv the heading "Organs of the Animal Body." 

 "By organ we understand, in accordance with the original 

 sense of the word organori (Werkzeug, instrument) any 

 body-part, cither internal or external of a multicellular 

 living being, (Lebeuesen) such part being of regular form, 

 regular position, and definite, intimate, histological struc- 

 ture, and having to perform instrumentally a special func- 

 tion or operation in behalf of the living individual as a whole, 

 this whole being designated an organism because composed 

 of such organs," etc. 



The naiveness here displayed lies in the recognition of 

 the term organ as going back in use and meaning to the 

 ancient Greeks, and in the same breath restricting its ap- 

 plication to multicellular organisms. When Aristotle recog- 

 nized that "each sense is confined to a single order of sensi- 



