AND ZOOGEOGRAPHY OF INDIAN OLIGOCH^TA. 147 



segments x-xi and xii-xiii respectively, and with an oesophageal 

 gizzard, are held to be the present-day representatives of "the 

 common ancestor. The Phreoryctidae are probably in turn to be 

 derived from the Lumbriculidse, where the number of gonads is 

 variable, and also their position; Lamprodrilus satyriscus has 

 three or four pairs of testes, and other forms — e, g., Luonbriculus 

 variegatHs—h.a,ve more than one pair of ovaries. 



But on the above hypothesis of the origin of the terrestrial 

 families of Oligochaeta we require as our starting-point a form 

 with a series of five pairs of gonads — three pairs of testes and two 

 pairs of ovaries ; while the discovery of Syngenodrilus makes it 

 probable that the ancestor of the Moniligastrid^ had no special 

 thickening of either oesophagus or anterior intestine — the gizzards 

 developed independently in the two subfamilies, in the Syn- 

 genodrilinae in front of and in the Moniligastridee behind 

 the testicular segments. It is obvious, therefore, that the 

 Phreoryctidse are already too specialized for our purpose ; the 

 ancestral form as here conceived has a lai^ger number of s'onads, 

 and is without an oesophageal gizzard. The ancestral group more 

 nearly resembled the Lumbricididae than the Pbreoryctid^ ; the 

 latter ai-e not in the direct line of descent of the earthworms. 



The Moniligastridfe, which, as Beddard has repeatedly insisterl, 

 retain many of the characters of the Limicoline section (clitellum 

 one cell only in thickness, non-union of the vasa deferentia of the 

 same side, vasa deferentia passing over only one segment), arose 

 independently of the other earthworms by the disappearance of 

 testes from seguient xi and of ovaries from xiii, and the con- 

 traction of the original segments x and xii to form testis sacs ; 

 while the common stem of the Megascolecidas, Glossoscolecidte, 

 and Lumbricidse originated by the disappearance of testes from 

 xii and ovaries from xiv, the lengthening of the vasa deferentia, 

 and the union of those of the same side. 



References to Literature. 



1. Beddard, P. E. — Descriptions of some new or little-kuowii Earthworms, 



tosetlier with an account of the Variations in Structure 

 exhibited by Per»o»j/a- e.i'cava^MS E. P. Proc. Zool Soc 

 1886, p. 298. 



2. ,, Note on the Pteproductive Organs of Monilic/aster. Zool. 



Anz., ix. 1887, p. 679. 



3. „ On tlie Structure of thi-ee new species of Earthworms .... 



Quart. Journ. Mic. Sci., xxix. 1888, p. 119. 



4. ,, On certain points in the Structure of Vrocliata 'E.V., awA. 



Dichogaster, nov. gen., with further remarks on the 

 Nephridia of Earthworms. Quart. Journ. Mic. Sci. 

 xxix. 1888, p. 235. 



5. ;, On the Homology between Genital Ducts and Nephridia in 



the Oligochsta. Proc. Roy. Soc, xlviii. 1890, p. '1.52. 



6. ,, Observations upon the Structure of a Genus of Oligochosta 



belonging to the Limicoline Section. Trans. Rov. Soc. 

 Edin., xxxvi. 1891, p. 7. 



10* 



