AND ZOOGEOGRAPHY OF INDIAN OLIGOCH.ETA. 



143 



one another) and correct the extreme displacements of the septa, 

 we get the following (the seminal vesicle may be neglected, as being- 

 only a diverticulum of the posterior testis sac) (text-fig. 17). 



Text-fip-ure 17. 



Sj/Hgenoclrilus, with the testis sacs separated from one another. 



The condition is similar to that in Desmogaster, except that the 

 spermathecse are a segment further back, and that there are three 

 pairs of prostates. If now we expand the testis sacs into segments, 

 we get a form with the following characters (text-fig. 18): — 



Text-fio-ure 18. 



VII y\n IX 



,n 



XI XII XIII XIV XV 



± 



Sijngenodrihis, with the testis sacs expanded so as to appear as segments. 



The figure is identical, except for the characters already mentioned, 

 with that of the " expanded '"' Desmogaster. 



Pi-obably neither text-fig. 15 nor 18 represents a form that 

 actually existed. In the first place, there is a gap of a segment 

 between the two pairs of testes; and in the second place, the 

 apertures of the spermathecse are separated by only one segment, 

 while those of the male apparatus are separated by two segments, 

 and hence the spermathecal apertures would not coincide with 

 the male pores of another worm in copulation. 



It has been pointed out b}^ Michaelsen (12) that in all the lower 

 families of Oligochseta the gonads follow each other in successive 

 segments; the ovarian segment immediately follows the testicular 

 segment or segments ; and the normal arrangement in the higher 

 families (testes in segments x and xi, ovaries in xiii) is to be 

 explained by the dropping-out of a pair of ovaries in xii. The 

 original condition — two pairs of testes followed by two pairs of 

 ovaries — still exists in the genus Haplotaxis ; and hence Michael- 

 sen (12, 17) and Beddard (9) look on this genus as the ancestor 

 of the higher Oligochseta. 



