SCATOLOGICAL STUDIES OF THE BIVALVIA (MOLLUSCA)
326
cross-section of the lumen of the rectum, which is bi-crescentic, owing
to the presence of a double longitudinal ridge, or typhlosole. The ribbons run to a knife-edge, of varying acuteness, at the margins, which
are usually folded over, either inwards or outwards. I n the ribbon of
faeces from which the drawings were made, one edge is folded inwards
and one outwards. (In turning over the specimen, it has been turned
both laterally and longitudinally.) This type of folding is seen very
frequently, and may even be more common than a folding inwards of
both margins. The central sulcus (seen from above) may be somewhat
indefinite at times. The characteristic shape of the ribbon is easily seen
with the naked eye, though a hand lens is useful for observing broken
fragments, etc. The consistency of the faeces is finely granular, the
surfaces of the ribbon being smooth. The colour, being determined by
that of the suspended matter ingested, varies considerably, but is
usually a dark chocolate brown, or more rarely slate. Sometimes the
faeces are almost white. Such white faeces have been noted almost
every spring in the tanks, for a period of a few days to a week. It has
been found due to the ingestion of a certain flagellate protophyte, which
appears in great numbers for periods such as those indicated, causing a
thick yellowish-white scum on the water, disappearing again as quickly
as it came.” (Dodgson, 1928, pp. 161-162, P1. 1, Figs. 3-7.)
“ The pellet is in the form of a ribbon, thickest a t the centre and
the two edges, and with these two edges rolled upwards and inwards
towards one another. The exact shape of the pellets seems to vary
somewhat, and in the case of a starved animal they may be thinner
and of abnormal shape. The ribbon is formed from fine detritus, with
the finest material in the lateral regions where it is closely packed,
while the coarser material lies in the central region and is looser. The
ribbon is thickened in the centre, and raised to form a mid-dorsal rib,
and lying under this on the ventral side is a wide shallow mid-ventral
groove, although the latter may sometimes be reduced or altogether
absent. The pellet together with certain modifications of it has been
described by Dodgson (1928). The faeces are fragile and easily damaged,
but the undistorted ribbon from an animal 8 cm long would average
1.5 mm in diameter, and may occur in lengths of 5 cm or more, tholrgh
usually breaking into much shorter pieces.” (Moore, 1931, p. 283, PI. 31.
Figs. 7, 8.) (Pellet-type 111-IOU).
28. Modiolus modiolus (L.)
“ The faeces are in the form of a ribbon of the same general type as
those of Mytilus, but with the mid-ventral groove much more pronounced : so much so, in fact, that the whole ribbon usually assumes t’he
326
cross-section of the lumen of the rectum, which is bi-crescentic, owing
to the presence of a double longitudinal ridge, or typhlosole. The ribbons run to a knife-edge, of varying acuteness, at the margins, which
are usually folded over, either inwards or outwards. I n the ribbon of
faeces from which the drawings were made, one edge is folded inwards
and one outwards. (In turning over the specimen, it has been turned
both laterally and longitudinally.) This type of folding is seen very
frequently, and may even be more common than a folding inwards of
both margins. The central sulcus (seen from above) may be somewhat
indefinite at times. The characteristic shape of the ribbon is easily seen
with the naked eye, though a hand lens is useful for observing broken
fragments, etc. The consistency of the faeces is finely granular, the
surfaces of the ribbon being smooth. The colour, being determined by
that of the suspended matter ingested, varies considerably, but is
usually a dark chocolate brown, or more rarely slate. Sometimes the
faeces are almost white. Such white faeces have been noted almost
every spring in the tanks, for a period of a few days to a week. It has
been found due to the ingestion of a certain flagellate protophyte, which
appears in great numbers for periods such as those indicated, causing a
thick yellowish-white scum on the water, disappearing again as quickly
as it came.” (Dodgson, 1928, pp. 161-162, P1. 1, Figs. 3-7.)
“ The pellet is in the form of a ribbon, thickest a t the centre and
the two edges, and with these two edges rolled upwards and inwards
towards one another. The exact shape of the pellets seems to vary
somewhat, and in the case of a starved animal they may be thinner
and of abnormal shape. The ribbon is formed from fine detritus, with
the finest material in the lateral regions where it is closely packed,
while the coarser material lies in the central region and is looser. The
ribbon is thickened in the centre, and raised to form a mid-dorsal rib,
and lying under this on the ventral side is a wide shallow mid-ventral
groove, although the latter may sometimes be reduced or altogether
absent. The pellet together with certain modifications of it has been
described by Dodgson (1928). The faeces are fragile and easily damaged,
but the undistorted ribbon from an animal 8 cm long would average
1.5 mm in diameter, and may occur in lengths of 5 cm or more, tholrgh
usually breaking into much shorter pieces.” (Moore, 1931, p. 283, PI. 31.
Figs. 7, 8.) (Pellet-type 111-IOU).
28. Modiolus modiolus (L.)
“ The faeces are in the form of a ribbon of the same general type as
those of Mytilus, but with the mid-ventral groove much more pronounced : so much so, in fact, that the whole ribbon usually assumes t’he