112 DR. J. STEPJIENSON ON THK MORPHOLOGY, CLASSIFICATION, 



References to Literature. 



1. MiCHAELSEN, W. — Oligoclia'ta, in : Diis Tierreicli. Berlin, 1900. 



2. „ NeneOligoeliaeten uiid neueFundovtealt-bekauiitev. Mitth. 



Naturbist. Mus. Hamburg, vol. xix. 1902. 

 3 jj !)ie geograpbische Verbreitiing der Oligocbaten. Berlin, 



190,3. 



4. J, Tbe OligocbfBta nf India, Nepal, Ceylon, Hnrma. and tbe 



Andaman Islands. Mem. Ind. Mus., vol. i. 1909. 



5. „ Die Oligocbaten-fauna der vorderindiscb - ceyloniscben 



llegion. Abli. Naturw. Vereiii Hamburg, vol. xix, 1910. 

 6 Oligocliaten, in : Ergebnisse der zweiten deutschen Zentral- 



Afrika-Expedition 1910-1911. Leipzig, 1915. 



7. Stephenson, J. — On a collection of Oligoebseta mainly from Nortbern India. 



Rec. Ind. Mus., vol. x. 1914. 



8, „ On some Indian Oligocbaita, mainly from Soutbern India 



and Ceylon. Mem. Ind. Mus., vol. vi. 1915. 

 9_ j^ On a collection of Oligocbaita belonging to the Indian 



Museum. Rec. Ind. Mus., vol. xii. 1916. 

 ]_0. ,, On a collection of OligocbiBta from various parts of India 



and Further India. Rec. Ind. Mus., vol. xiii. 1917. 

 W^ ,j On a collection of Oligoclneta from the lesser known parts of 



India and from Eastern Persia. Mem. Ind. Mus., vol. vii. 



1920. 



II. — O.Ni POLYPHYLY IN THE OlIGOCH.ETA. 



The material which I wish to use in this discussion is derived 

 from the Megascolecidse, and largely from the subfamily Mega- 

 scolecinfe. It will be necessary first to show liow the various 

 genera of this subfamily are related (v. text-fig. 1). 



The whole of the family Megnscolecida? is to be. derived from 

 an original form which has essentially the characters of the genus 

 Notioclrilus as defined by Michaelsen in the Tierreich volume of 

 1900. These are : Testes and funnels two pairs, free in seg- 

 ments X. a.nd xi. ; vasa deferentia of each side uniting in their 

 backward course so that there is only one pair of male apertures, 

 on xviii. ; two pairs of tubular prostates, with unbranched central 

 canal, opening on xvii. and xix.; setae four pairs per segment; 

 one pair of meganephridia per segment; a single gizzard far 

 forward, in segment v. or vi. 



The Megascolecinse, however, take their origin from a form 

 which is one remove from this — Diplotrema, in wliich the anterior 

 pair of prostates have disappeared and the posterior pair of 

 prostatic pores have moved forwards to open on xviii. near «fche 

 apertures of the vasa deferentia. 



In Plutellus, the first genus of the Megascolecina?, the prostatic 

 pores have fused with the openings of the vasa deferentia on 

 xviii. so that there is but one pair of pores; and this remains 

 throughout the subfamily as its distinguishing character. In the 

 remaining genera the changes are of three cliief kinds — the setae 

 may takeon the perichpetine ari^angement, the four pairs multiply 

 in number and become spread out to form a more or less com- 

 plete ring round each segment ; the nephridia may be broken up, 



