110 OLIGOCHAETA 



times smaller ; in Perichaeta taprobanae, for example, the spermiducal gland is so 

 small as to be entirely contained within one segment ; in other species of Perichaeta 

 it extends through a considerable number of segments. The peculiar appearance of the 

 gland is produced by the branching of its lumen ; the tubes are lined by low columnar 

 epithelium which does not appear to be ever markedly glandular in character ; 

 attached to the tubes are groups of pear-shaped cells massed into bundles, whose fine 

 processes seem to open into the lumen between the non-glandular cells which line it. 

 It is this division of the lumen coupled with the grouping of the glandular pear- 

 shaped cells that gives its peculiar appearance to the spermiducal gland in the 

 Perichaetidae, &c. The whole organ is covered with a fine covering of peritoneum. 

 It will be evident from the figures illustrating the minute structure of the glands 

 (woodcut, fig. 31) that there is no essential difference between this type and the tubular; 

 the difference lies in the fact that in the Perichaetidae the single tube has become 

 branched and the glandular lining has become grouped instead of remaining a con- 

 tinuous layer ; we find that genera very nearly allied in other particulars differ as to 

 whether they possess a tubular or racemose spermiducal gland ; besides, as I have 

 pointed out, there are among the Perichaetidae glands which seem to be intermediate 

 between the two extremes ; the branching is much reduced and as a consequence the 

 breaking up of the glandular cells into groups is not so marked. 



In the case of both kinds of glands the relations of the sperm-duct are pecu- 

 liar ; it never opens into the glandular part. As a rule the opening is into the 

 muscular duct just at its commencement ; this rule has apparently no exceptions 

 in the Perichaetidae (see, however, the remarks upon Perichaeta ceylonica, below) ; 

 it is, however, not so common among those genera which have the tubular variety 

 of the gland ; in Pontodrilus the sperm-duct has these relations ; but in no member 

 of the family Acanthodrilidae has the sperm-duct any direct connexion with the terminal 

 gland at all. In every species it even opens on to a segment distinct from that 

 which bears the orifice of the these ; between this extreme and the other there are 

 various intermediate stages ; thus in Microscolex novae-zelandiae the sperm-ducts 

 open into the spermiducal gland just before the latter opens on to the exterior ; in 

 Typhaeus the orifices are separate but are situated upon the same segment. There are 

 as a rule but a single pair of glands in the Megascolicidae ; but exceptions are known ; 

 thus with the exception of Acanthodrilus monocystis the Acanthodrilidae have always 

 two pairs opening on to the seventeenth and eighteenth segments ; two pairs also 

 characterize the genus Gordiodrilus. In the latter case they are in consecutive 

 segments ; a unique disposition of the glands is afforded in the aberrant species of 

 Perichaeta P. ceylonica; there are here two pairs, which are in the same segment 



