^38 Mr, H. E. Strickland on the Structure and Affinities processes, and with this remarkable difference ; that while in the latter the cilia propel the water outwards, sending off a current at their apices ; in the tentacula, on the contrary, the cilia are di-rected downwards, drawing in and sending a current of water down their whole surface. This is exactly what we might be led to expect in the olfactory organs, and forms a beautiful compen-sation for the power of drawing a current of air through the nostrils in the higher animals. Upon the whole, therefore, we think that little doubt can remain of the real function of these organs. P.S. Since writing the above, we have seen M. Quatrefages^ elaborate paper on his Eolidina paradoxum in the ^ Annales des Sciences Naturelles,^ and are happy to find that many of his ob-servations agree with our own. His Eolidina we consider to be undoubtedly an Eolis very nearly allied to our E. angulataj MS., communicated to the last meeting of the Association. In the position which he assigns to the anus at the posterior end of the large central vessel of the gastro-vascular system, we conceive him to be under a mistake, deceived probably by the ap-parently abrupt termination of that vessel. The real anus, we have no doubt, will be found at the side, as in other species of this and the allied genera. He appears also to have misunderstood the organs of vision, which, it can scarcely be doubted, are as complete as in other species of Eolisy as well as in Polycera, Goniodoris and MelibceUj in all of which a lens is distinctly visible ; he however figures and describes the eye in his Eolidina as merely a broad convex expansion of the retina and pigmentum nigrum. It would ap-pear from his drawing that he has mistaken the auditory capsule for the optic ganglion or a swelling of the optic nerve, otherwise he has entirely overlooked the organ of hearing. His descrip-tion of the generative organs is quite at variance with the well-known peculiarities of this order. M. Quatrefages^ remarks on zoological affinities are ingenious : on this interesting portion of the subject however we cannot at present enter, but hope to do so on a future occasion, when a further investigation of the subject shall have enabled us to speak â– ^ith more certainty than we can possibly do at present. XXIX. — On the Structure and Affinities of tJpupa, Lin., and Irrisor, Lesson. By H. E. Strickland, M.A.* The African continent presents us with several species of birds constituting a well-marked genus, to which Lesson in 1831 ap-* Read to the Zoological Section of the British Association at Cork, Au-gust 19, 1843 ; and communicated by the Author,
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