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Show 532 DR. G. E. DOBSON O N T H E [June 20, of the presence of prehensile organs resembling the sucking-disks Cephalopoda. On the inferior surface of the thumb, from the base of the first phalanx, and from the sides of the metacarpo-phalangeal joint, corresponding to the position of the ball of the thumb in other Bats, arises by a short peduncle a circular hollow suctorial disk about one tenth of an inch in diameter (Plate LV. fig. 5, enlarged). On the sole of the foot a similar but considerably smaller disk (fig. 6) is placed, not in the same relative position, however, as on the thumb ; for it covers the metatarsal bones, not the bases of the first phalanges of the toes. In a paper published in the ' Boletin revista de la Universidad de Madrid,' by Senor Jimenez de la Espada, a member of the Spanish Expedition to explore the natural productions and physical conditions of South America, the author relates his observations on the habits of this species, and describes the sucking-cups. I have not been able to procure a copy of this paper; but fortunately a full abstract of the part relating to Thyroptera tricolor is given in the ' Zoological Record ' for 1870, as follows :- "The sucking-cups consist of a coriaceous disk; they are little hemispheres, hollow, flexible, and extremely movable, on the first phalanges of the thumbs of the wings and near the heels on the soles of the feet. They were used by the animal to fasten itself to the fingers as it tried to bite, producing the same feeling as a key or thimble when applied to the tongue after sucking out the air. These cups are deep, membranaceous on the edge, fleshy in the centre, those on the wings larger than those on the feet. The muscular arrangement is such as to allow the animal to vary the diameter of the organ ; and by their means the animals attached themselves to the sides of the box in which they were kept, although, when sleeping, they suspended themselves by the claws like other Bats." With the latter part of the above statement, referring to a muscular arrangement in a sucking-disk, I am quite unable to agree. Microscopical sections of the disk made in every direction failed to exhibit the slightest trace of muscular fibre; and I believe that the animal does not possess the power of varying the diameter of the organ by direct muscular agency. Indeed the presence of a muscular arrangement in the sucking-disk of Thyroptera tricolor, such as Sehor Jimenez de la Espada refers to, would be a most remarkable anomaly ; for this species would possess special muscles of which not the slightest homologue could be found in any other vertebrate animal. But nature does not form complicated organs where simple ones are equally or sufficiently effective. The remarkable sucking-cups of Thyroptera are evidently but highly differentiated conditions of the integuments and superficial fascia of the balls of the thumbs and soles of the feet. This is shown by their position, by their structure, and by the presence in other Bats of analogous conditions of the same parts, which must be also considered homologous. In Vesperugo nanus, Ptrs., V. tylopus, Dobson (Plate LV. figs. 1 & 3), and especially in V. pachypus, Temm. (fig. 2), the sole of the foot is very broad, slightly concave, and almost circular in outline, so |