d opens on the dorsal surface. Within the stomach, there can generally
be plainly seen, in accordance with the period of digestion when the
specimen was taken, a thin, yet strong, perfectly transparent epithelial
membrane, not exhibiting under the highest power of the microscope any
structure: it enters the branching caeca, and extends from the edge of
the bell of the oesophagus to the commencement of the closed rectum, and
consequently terminates in a point: it consists of chitine, like the
outer integuments of the animal, and by placing the whole body in
caustic potash, I have dissolved the outer coats of the stomach, and
seen the bag open at its upper end, perfectly preserved, floating in the
middle of the body, and full of the debris of the food. In most of the
specimens which I have examined, preserved in spirits of wine, this
epithelial lining was some little way distant and separate from the
coats of the stomach; and hence was thought by M. Martin St. Ange to be
a distinct organ, like the closed tube in certain Annelids.
Occasionally, I have seen one imperfect epithelial bag or tube within
another and later-formed one. Digestion seems to go on at the same rate
throughout the whole length of the stomach; if there be any difference,
the least digested portions lie in the lower and narrower part. The
prey, consisting generally of crustacea, infusoria, minute spiral
univalves, and often of the larvae of Cirripedes, is not triturated: when
the nutritious juices have been absorbed, the rejectamenta are cast out
through the anus, all kept together in the epithelial bag, which is
excluded like a model of the whole stomach, with the exception of that
part coated by the bell of the oesophagus. I have sometimes thought that
the bag was formed so strong, for the sake of thus carrying out the
excrement entire, so as not to befoul the sack. I believe Lepas can
throw up food by its oesophagus; at least, I found in one case, many
_half-digested_ small Crustaceans in the sack, and others of the same
kind in the stomach.

_Circulatory System._--I can add hardly anything to what little has been
given by M. Martin St. Ange: like others, I have failed, as yet, in
discovering a heart. The whole body is permeated by channels, which have
not any proper coat: there is one main channel along the ventral surface
of the thorax, dividing and surrounding the mouth, and giving out
branches which enter the inner of the two channels in each cirru