234 
pair of tumid lips between which is the narrow opening 
of the neuropodial setal sac which contains the crotchets. 
The external opening of the sixth (last) nephridium is just 
behind the dorsal end of the ninth neuropodium. x 6. 
Fig. 20. Ventral stem of gill of younger Laminarian 
worm. This stem is about half the length of that shown 
in the preceding figure, and its lateral branches are still 
comparatively simple. x 20. 
Fig. 21. Lateral branch, from one of the dorsal stems 
of the gill shown in fig. 19, bearing twenty-two gill 
filaments. x 20. 
Fig. 22. Fourth right gill of a littoral specimen 
about 110 mm. long. The gill consisted of ten main 
stems, eight of which have been cut away. The blood- 
vessels are seen traversing the basal membrane. The 
lateral twigs are fewer in number and not so richly 
branched as in Laminarian specimens. xi 20: 
Prac te 
Fig. 25. Dissection of a large Laminarian specimen 
(250 mm. long) cut open along the mid-dorsal line to show 
the anatomy. ‘The alimentary canal is pushed over to the 
left side, and most of the tail has been cut out. The 
proboscis is about half extruded. The dorsal portion of 
rach left gill is seen. The gastric plexus is shown full of 
blood, and the heart about half expanded. ‘The funnel 
only of the first left nephridium is seen, the rest of the 
organ being covered by the esophagus. The funnel of 
the third left nephridium is hidden by one of the 
csophageal glands. The funnel of the fifth right nephri- 
dium has pushed its way through the interval between two 
of the oblique muscles. The blood-vessels of the sixth 
right nephridium have been pushed forward one annulus, 
