15 
The curious proper musele (byssus-muscle?) of the organ Mb, Mb’ 
has been noticed in the foregoing chapter. 
ERTE ROOT 
is enelosed in the longitudinal median ventral groove above men- 
tioned. This groove begins a very short distance behind the mouth 
and merges into the posterior opening by which both the contents 
of the intestine and of the genital glands are evacuated. 
The very foremost portion of the ventral groove is externally 
discernable as a short longitudinal slit (fig. 3, f; fig. 28, s) of more 
considerable depth than all the rest of the groove, and was noti- 
ced above. It leads into a system of elongated slits and cavities 
of more or less width, very strongly eiliated and in communica- 
tion with each other (fig. 28, cc). These slits ramify like a tree 
short eiliated ducts springing from them in different directions. 
The whole has the appearance of a secreting gland, with an in- 
ternal surface for the greater part ciliated and with a delicate 
stroma of connective tissue supporting both the superficial and the 
deeper situated secreting cells. 'The cells have a transparent, granu- 
lar protoplasm, a distinet nucleus and very much resemble the cells 
hereafter to be mentioned which are figured in 25 and 26. There 
can be no doubt that a glandular function must be ascribed to 
this structure, which I would propose te designate by the name of 
anterior footgland. | 
The whole of the anterior footgland is situated under the hinder 
portion of the oesophagus and has already disappeared in the re- 
gion where the stomach commences. It appears to be more or less 
sloping upwards and forwards anteriorly, whereas posteriorly its 
constituent cells do not appear to be histologically very much differ- 
ent from those that are direetly contiguous with it and accompany 
the foot as a cushion right and left, down to the other extremity 
of the body. I propose to call this latter elongated symmetrical 
gland (fig. 24, fg) which , though composed of much the same elements 
can still be very well distinguished from the one just described: 
the posterior foot-gland. In it no ciliated cavities can be distin- 
