362 Records of the Indian Museum. [Vol. XIII, 



chaetella. It might be derived from Plagiochaeta ,— or rather from 

 Perieodrilus, a genus under which Michaelsen has placed those 

 species, originally grouped as Plagiochaeta by Benham, which have 

 the nephridiopores in the same line on each side (the type of the 

 genus Plagiochaeta has them in two rows, alternating in succes- 

 sive segments). Perieodrilus has the acanthodriUne arrangement 

 of the posterior male organs and is meganephric, but has the 

 perichaetine arrangement of the setae ; it is in fact removed from 

 Notiodrilus only by the development of the setae in rings instead 

 of in pairs. From such a form Hoplo chaetella differs in the partial 

 breaking up of the nephridial system and the amalgamation of the 

 openings of the vas deferens and anterior prostate. 



If we take the first hypothesis, as I did for Erythraeodrilus 

 previously, we find that we are in the presence of an element of our 

 fauna which has relations with Madagascar ' (the home of Howas- 

 colex). To some extent this is confirmed by the localities where 

 Hoplochaetella and Erythraeodrilus have been found, — on the west 

 coast of India. Bourne's Pmc/^ae^a stuarti was found, certainly, 

 about 160 miles from the Malabar coast, — indeed nearer to the east 

 than the west coast of the peninsula ; but some of the present 

 species were discovered actually on the shore, and seem to be 

 euryhaline, — able to withstand the action of salt water, — and 

 hence, probably, to endure a journey by sea {of. the discussion by 

 Michaelsen of the possible spread of Microscolex by the West-wind 

 drift in the Southern Ocean, 12, 15, 16) ; the South-west monsoon 

 blows steadily in the required direction for several months of every 

 year. There is of course also the possibility that the introduction 

 is of comparatively ancient date, by means of the land connec- 

 tion during the earlier Tertiary period. 



On the second hypothesis Hoplochaetella will have had an 

 Australasian origin. This is the present view ; hitherto Hoplo- 

 chaetella and Octochaetus have been the two genera common to 

 India and New Zealand, — the indications of a communication 

 between the two lands which probably at one period did not include 

 Australia. The position is not very different if we suppose Hoplo- 

 chaetella to be non-existent in New Zealand but to be derived from 

 the New Zealand genus Perieodrilus. 



Merely from the point of view of practical convenience, the 

 first arrangement of the phylogenetic tree is preferable. As I have 

 previously pointed out (19), the Erythraeodrilus branch can thus 

 without difficulty be included in the Octochaetinae, by making the 



1 Though Wallace, as is well known, gave up the theory of the existence of 

 a former "Lemuria," — a large tract of land including Madagascar, India, and 

 Malaya, — and came to believe in the comparative fixity of the great land-masses 

 of the globe (compare the view in his " Malay Peninsula " and " Island Life") 

 later authors are not so conservative. Thus Gadow (9) supposes a permanent 

 connection between Madagascar and India from Primary times up to the Oligo- 

 cenc, breaking up in late Oligocene ; Deperet (8) supposes the connection between 

 India and Madagascar to have been broken towards the end of the Cretaceous, 

 but re-established during the Tertiary period ; for the geological argument see, 

 for example, Sucss (21, \ol. i, p. 417). 



