110 OLIGOCHAETA 



times smaller ; in Perirhaeta 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 chai-acter; 

 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 illusti-ating the minute structure of the glands 

 (woodcut, fig. 31) that there is no essential diflference 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 



