60 OLIGOCHAETA 



elsewhere columnar. In the genus Pontoscolex and in most other genera each of the 

 three or more pairs of glands opens by its own separate orifice into the oesophagus. 

 Lumbricus (including Allolobophora) is an exception to this statement ; in that genus, as 

 was at first pointed out by MARSHALL and HURST in their ' Practical Zoology,' the first 

 pair of glands alone open into the lumen of the gut ; the two following glands of each 

 side open into each other and into the lumen of the first pair ; there is thus but a single 

 orifice into the gut for all three glands ; this difference has been emphasised by terming 

 the first pair of glands oesophageal pouches in contradistinction to oesophageal glands. 

 The descriptions of MARSHALL and HURST have been confirmed by KULAGIX (1). One 

 other genus at any rate shows the same thing exactly ; I have found that in Microdrilus 

 there are three pairs of glands of which the first pair only open into the gut; the 

 remaining two of each side open into the first. A curiously analogous arrangement 

 was found occasionally to exist in Polytoreutus ; MICHAELSEN discovered that in 

 a specimen of Polytoreutus coeruleus the last of the unpaired glands opened not 

 directly into the oesophagus, but into the pouch in front. 



An example of the calciferous glands of this type, which are, it will be observed, 

 not distinctive of any one family, is afforded by Octochaetiis multiporus (see Plate V). 

 In the young- just ready to leave the cocoon the glands, which are most conveniently 

 studied in that condition, owing to their small size, form merely a dilatation of the 

 oesophagus. In a series of sections commencing at the head end of the worm the gland 

 comes into view lying above the oesophagus and between the two dorsal vessels ; the 

 latter immediately come to lie upon it. Still passing back, the gland gradually extends 

 round the oesophagus opening into it at first in the dorsal middle line, afterwards 

 along other lines. Ultimately the openings into the oesophagus become so frequent 

 that the latter can be no longer distinguished from the surrounding gland ; its somewhat 

 more columnar epithelium passes gradually into the lower cubical epithelium of the 

 gland. Only on the ventral surface can the oesophagus be said to exist apart from 

 the gland for there are no ventral folds of the glandular membrane. The entire gland 

 is covered with a layer of peritoneum of which the cells are not so long and pear-shaped 

 as elsewhere. The lining epithelium is arranged in numerous folds some penetrating 

 further towards the lumen than others and being generally thicker at their free edge 

 owing to the fact that the cells are here more columnar. Peripherally the cells are 

 ciliated. 



The secretion produced by these glands is in the form of solid particles of calcareous 

 matter; the actual form in which these concretions occur varies somewhat. In 

 Lumbricus they are figured and described by CLAPAREDE as being 'small perfectly 

 spherical bodies with a diameter of from 2-6 micromm.'; in optical properties they 



