136 MISS G. SWEET ON THE SPERMIDUCAL 
Summary. 
It will be seen from the above description that there is, in 
these species, a continuous series of forms of increasing com- 
plexity in internal structure. Commencing with the tubular 
forms, we have first those in which the gland-cells open into the 
lumen between the columnar cells of the lining (PI. 14. fig. 16). 
There is here obviously a very close resemblance in structure 
to the clitellum or to the special accessory gland in 
Megascolides intermedius and M. attenuatus, if we neglect the 
occurrence of the muscle-layers there. Next we have those 
forms in which perhaps, on account of the increase in cornifica- 
tion of the lining epithelium, the gland-cells open into the lumen 
in groups (PI. 15. fig. 17). The next stage is seen in such a 
form as Digaster excavata, where the lumen gives out a single 
series of branches, each of which bears at its end a group 
of gland-cells, which is thus situated at about half the thickness 
of the gland-wall. Here, however, the columnar lining of the 
main duct is not continued up these branches (cf. Digaster 
excavata). 
Further complication is met with in such forms as Megasco- 
lides illawarre and Megascolex dorsalis, where the main duct all 
along its length branches considerably more than in Digaster 
excavata, and here to a great extent the branches are lined by 
cubical cells continuous with the columnar lining of the main 
duct (Pl. 15. fig. 24); but here also there is no cell-lning to the 
fine terminations of the branches. From these we pass to such 
highly complex forms as, for example, Megascolex tasmanica, M- 
Frenchi, in which the main duct breaks up immediately it enters. 
the gland, so that there is no central tube in these lobate forms 
(Pl. 15. figs. 19 & 20). Corresponding with this, the branching 
is still further increased, and as a result the lobules become more 
closely compacted together and fill up the entire interior of the: 
gland. Consequent on this increase in branching, the groups. 
are much more numerous and are pushed out towards the peri- 
phery, so that the mass of the gland is made up of these groups, 
the cells in which become more closely pressed together and 
their ducts much shortened. The blood-vessels which originally 
ran along the surface of the gland, or just outside the lining of 
the duct, have become much branched corresponding with the 
branching of the duct, and serve very often, with the small 
