( 735 ) 



XIV. — On Intestinal Respiration in Annelids; with Considerations on the Origin 

 and Evolution of the Vascular System in that Group. By J. Stephenson, 

 M.B,, D.Sc. (Lend.), Major, Indian Medical Service, Professor of Biology, 

 Government College, Lahore. 



(MS. received August 29, 1912. Read March 17, 1913. Issued separately November 7, 1913.) 



CONTENTS. 



I. Oligoch^ta. 



1. The phenomena of antiperistalsis and 

 ascending ciliary action in the 

 intestine of aquatic Oligochfeta . 



736 



Summary 744 



Exceptions to the general rule . . 745 

 On the possiljle descent of Chxtogaster 



from parasitic ancestors . . 745 

 2. The contractions of the alimentary wall 

 in the aquatic Oligochseta in 

 relation to those of the vascular 

 system 748 



3. The evolution of the vascular system in 



the Annelida .... 766 



4. The theories of Lang and Vejdovsky . 776 



II. POLYCH^TA. 



1. Historical .783 



2. Observations on Polychfeta . . . 791 



Addendum on similar phenomena in 



other groups .... 808 

 Summary 809 



3. The bearing of the observations on 



Putter's theory . . . .814 

 General Considerations . . . 816 



III 



References to Literature 



827 



The investigations recorded in the present paper have been carried out at various 

 times during the last six years. A number of the observations on aquatic Oligochseta 

 were made some time ago in India, and, along with some of the theoretical conclusions, 

 formed Part IV. of a Thesis ("Studies on the Aquatic Oligochseta of the Punjab") 

 presented in 1909 for the D.Sc. degree of the London University. This division of 

 the paper has been considerably extended as a result of further investigations on Indian 

 freshwater forms, and on the littoral Oligochseta of the Clyde, the latter carried out 

 at Millport in 1909. The portion of the present paper which is concerned with the 

 Polychseta and smaller groups represents work done in 1909 at Millport, and in 1912, 

 during my occupancy of the London University table, at the Plymouth Laboratory. 



The observations on intestinal respiration in Oligochseta, especially those which 

 concern the relation of the antiperistaltic contractions of the gut to the contractions of 

 the dorsal vessel, led me, in conjunction with my investigations into the anatomy of 

 the circulatory system in these forms, to the views on the evolution of the vascular 

 system which are expressed in Section 3 of Part I. My original object in studying the 

 Polychseta was to find out whether the facts of anatomy and physiology in that group 

 supported these views. The observations which resulted, while in a general way con- 

 firmatory, add nothing to the argument ; and the consideration of the evolution of 

 the vascular system has therefore been left at the end of the part dealing with 

 Oligochseta, where it most naturally occurs. Certain phylogenetic speculations, on 



TRANS. ROY. SOC. EDIN., VOL. XLIX. PART III. (NO. 14). 101 



