Nachdruck verboten, 

 üebersetzungsrecht vorbehalten. 



An endeavour to show that the tracheae of the 

 Arthropoda arose from setiparous sacs. 



By 

 Henry M. Bernard, M. A. Cantab. 



With 3 woodcuts. 



Briefly stated, the problem we have here attempted to solve 

 is this: 



Certain Chsetopod Annelids migrated on to the land at an early 

 geological period, and are now represented by the ïracheata, so called 

 because of their breathing organs which are chitin-lined invaginations 

 of the outer cuticle; — whence came these respiratory organs? 



In the first place we feel fairly safe in affirming that they must 

 have arisen from some previous structures, which first assisted, and 

 ultimately by a gradual change of function monopolised, the respiration. 

 That the tracheœ are entirely new formations is very improbable. The 

 thickening of the cuticle which seems to have taken place early, per- 

 haps primarily as a protection against desiccation, would make it less 

 and less plastic for the formation of such purely ectodermal structures 

 as trachea'. We have then to ask, what structures were there in the 

 original ChcCtopod Annelid which were available for development into 

 tracheiii, and which will satisfy all the conditions? 



Some authors have suggested the nephridia, but this hardly sa- 

 tisfies all the conditions ; it does not, for instance, explain the diffuse 

 arrangement of the trachea} in Peripatus. Other writers, again, limit 

 themselves to the safer, because more indefinite derivation from dermal 



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