Note 293 — Chapter III

The sacculus is a cirripedia which lives in the condition of a parasite in the intestinal canal of certain crustacea. It represents the deepest retrograde transformation of a living being primarily of a higher organization. It has lost all its differentiated organs, and essentially only amounts to a vesicule (hence its name: little bag), which fills itself with juices from its host, absorbed by the parasite with the help of certain vessels, which it plunges into the intestinal walls of the latter. This atrophied creature has retained so few marks of an independent animal that it was looked upon for a long time as a diseased excrescence of its host’s intestines.