The intestine has a pair of caeca or two or three pairs (but all lie in one segment) in the genus Pheretima and in one species of Rhinodrilus.
In Benhamia caecifera and at least one other earthworm there are numerous caeca, one pair to each segment.
He was quite aware of the taxonomic value of the vocal organs of some groups of birds, presently to be especially mentioned, and he had himself ascertained the presence and absence of caeca in a not inconsiderable number of groups, drawing thence very justifiable inferences.
In addition to the musculature of the proboscis and proboscidian sheath, longitudinal muscular fibres are found in the walls of the oesophagus, whilst transverse ones are numerous and united into vertical dissepiments between the successive intestinal caeca, thus bringing about a very regular internal metamerization.
Cases of asymmetry or irregularity in the arrangement of the intestinal caeca, though sometimes occurring, are not normal.