244 THE PATH OF DEGENERATIVE EVOLUTION 



are homologous with mesonephric spaces ; but these 

 latter do not exist as genital chambers in higher 

 vertebrates. 1 



It must be noted that the homology between 

 mesonephric spaces and the genital spaces of 

 Amphioxus, as made by these writers, is not uni- 

 versally accepted. 



2. Plants. The Scophulariaceae, which have 

 usually four stamens, are derived from ancestors 

 which possessed five. Usually the fifth stamen is 

 only represented by a tiny process which rapidly 

 atrophies. However, in Pentstemon the fifth or 

 posterior stamen is developed, not as a functional 

 stamen, but as a staminode, the' function of which is 

 to stretch open the flower to make it accessible to 

 hymenopterous insects with short probosces. 



Can it be said that in such cases a rudimentary 

 organ has really become redeveloped to assume a 

 new function ? To establish this it would be 

 necessary to show in the case we have just 

 mentioned, that the stamen did not become trans- 

 formed directly into a staminode, but that it first 

 became rudimentary and then developed afresh into 

 a staminode. 



An interesting fact is, that in some hybrid 

 varieties of Pentstemon the staminode becomes fertile 



1 Boveri, Die Nierencatialclien der Amphioxus. (Zool. Jdhrbuch. 

 Abih. Anal, und Ontogenie der Thiere, vol. v., 1892.) 



Wiedersheim, Grundzilge der Vergleichenden Anatomie der Wir- 

 belthiere. Jena, 1893. 



