230 PROCEEDINGS OF THE AMERICAN ACADEMY. 



tube differ much in regard to the details of structure, they agree in the 

 one notion, that Leydig's fibres are tubes. Most of the advocates of this 

 view ascribe to these fibres no definite function. 



Thirdly, that advanced by Kowalevsky ('71), which makes these 

 structures supporting organs, homologous to the chorda dorsalis of verte- 

 brates, and denies to them any nervous nature whatever. 



Fourthly, the view advocated by Vejdovsky ('84), which maintains 

 the supporting nature of Leydig's fibres, but denies to them any genetic 

 relationship to the chorda dorsalis of vertebrates. The relationship is 

 one of analogy alone, since Leydig's fibres are derived from mesoderm, 

 whereas the chorda dorsalis of vertebrates comes from entoderm. This 

 view agrees with the third in denying all nervous nature to Leydig's 

 fibres. 



Fifthly, the idea advanced by Eisig ('87), which is that Leydig's fibres 

 and the giant cells connected with them are in the young stages of the 

 worm nervous in nature, but that later they undergo degeneration, and 

 that the fibres finally come to function as a supporting organ. Thus 

 they may in the adult worm be compared functionally with the chorda. 

 He further suggests a comparison of these structures with the white 

 matter of the nervous system of vertebrates, saying ('87, p. 483), " Auf 

 Eine von mir schon im Vorhergehenden betonte Thatsache mochte 

 ich aber bei dieser Frage nach der Bedeutung der Neurochorduerven 

 noch einmal zuriickkommen, well sie moglicherweise mit zum besseren 

 Verstiindnisse beitragen kann : ich meine die Thatsache, dass wir im Ner- 

 vensysteme der Anneliden fortan zwei Bestandtheile zu unterscheiden haben. 

 Den einen bildete das dauernde, aus feinsten Fibrillen und zahlreichen 

 Meinen Ganglienzellen sick atifbauende System, den anderen bildet das 

 allmdhlich der Degeneration unterliegende, aus breiten Nervenfasern und 

 wenigen riesigen Ganglienzellen zusammengesetzte. Die Elemente des 

 ersteren Bestandttheiles wurden in Anbetracht ihres histologischen Ver- 

 haltens ofters der 'grauen Substanz ' der Vertebraten-Centren verglichen 

 — vielleicht diirfen wir diejenigen des letzteren der ' weissen Substanz ' 

 gegeuiiberstellen." 



Finally, there are those who deny to Leydig's fibres any nervous 

 nature, on the ground that these fibres do not react to the Golgi method. 

 These writers do not commit themselves to any definite statement as to 

 the function of the structures in question. 



The following lists give, in chronological order, the chief supporters of 

 these various theories : — 



