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.
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.
The existence of paired caeca was previously known in a few armadillos and anteaters, but Dr Mitchell has shown that they are common in these groups, while he has also recorded their occurrence in the hyrax and the manati.
The absence of such renal caeca in Limulus and their presence in the terrestrial Arachnida is precisely on a parallel with their absence in aquatic Crustacea and their presence in the feebly branchiate Amphipoda.
The intestine is provided with numerous branched caeca in Aphrodite.
Sal, Prosomatic pair of gastric caeca in Scorpio, called salivary glands by some writers.
Canal sometimes with protrusible proboscis; never with gizzard or oesophageal glands; intestine with caeca as a rule.
On its inner surface the longitudinal canal is adpressed to the lateral bloodvessel, and gives off a number of small, blind caeca or tags, each of which ends in a small clump of cells.
Renal excretory caeca (Malpighian tubes) are developed from the proctodaeum (not from mesenteron as in scorpion and Amphipoda).
Fine caeca of the nephridium, which are seen ramifying transversely over the whole inner surface of the pedal muscular mass.