they ought not to figure on the list of paupers. We have found the orifice of the _Tubicinella_ covered with cyami of every age, and their abundance in this place seems to indicate that their food was not supplied to them by the skin of their host. Mons. Ch. Lutken has recently published a very interesting monograph on these curious animals; according to him the _Cyamus rhytinæ_, which was thought to proceed from a piece of the skin of a _Stellerus_, appears to have been found on the skin of a whale. The Picnogonons, the nature as well as the kind of life of which has been so long time problematical, deserve to be ranked among messmates, at least during their youth; in fact, after being hatched, they live on the _Corynes_, the _Hydractiniæ_, and other polyps, while at a later 35 period they frequent molluscs or higher classes; Allman mentions the case of a _Phoxichilidium coccineum_ lodged in a _Syncoryne_. There are, perhaps, many other crustaceans which, placed among messmates, like the _Pandarus_ and others, would have a right to claim a further inquiry. It is a fact that they are never seen except on the skin of their host, where they are always visible, preserve their colours entire, and never change their costume for the undress of a parasite. The _Pandari_ live especially on the _Squalidæ_. Some which are found in our seas are of rare elegance of form. We must, perhaps, place among messmates the crustacean which Siebold found in the Adriatic, at Pola, on the belly of the worm _Sabella ventilabrum_, and it is not impossible that the _Staurosoma_ observed by Will on an actinia, should have its place here rather than among the parasites. A Rotifer without vibratory ciliæ, the _Balatro calvus_ of Claparède, lives as an epizoon on the same annelids which lodge the Albertia in their interior. The Darwinists, observes Claparède, will not fail to remark the presence of these Rotifers of the genus Albertia in the interior of the animal, and of the genus Balatro on the exterior. The parasite Balatro, like a shadow, never quits his Mecænas, says the learned naturalist of Geneva; who has observed it on the _limicolous Oligochæts_ of the Seime, in the Canton of Geneva. The _Nebalia_ of Geoffroy is an interesting crustacean, abundant on the coast of Brittany. This charming animal gives lodging habitually to a messmate which Mons. Hesse considered as an animal allied to the 36 _Histriobdellæ_, but which is only an imperfectly described Rotator. We believe that it is the same animal to which Professor Grube has given the name of _Seison nebalia_. It appears to assume the aspect of the Histriobdellæ, and may perhaps be adduced as an example of mimicry.