OCR Text |
Show 1894.] TELEOSTEAN MORPHOLOGY. 431 what was presumably its original relationship to the morphologically ventral side of the eye. Dr. Giinther considered that the structure he described might represent a saccus lacrymalis, but I do not see there is any reason to regard the recessus of flat-fishes in that light. The saccus is a superficial structure developed altogether outside the eye, never acquiring any but a topographical (and physiological) relationship therewith. It is always in intimate relationship with the lacrymal scute ; but no flat-fish with which I a m acquainted possesses anything that can be homologized with this scute, while such other fishes as I have examined, which do exhibit structures to which that name has been applied, show no trace of an accessory visual organ. Tbe lacrymal gland suggested itself to m e at one time as a possible homologue; but beyond a certain similarity of position, of innervation, and of blood-supply, there is little evidence in favour of this hypothesis either. The lacrymal gland arises in Mammalia as a solid outgrowth of the conjunctival epithelium into the underlying connective tissue, subsequently becoming hollowed out to form the cavities of the gland find ducts 1, and never enters into any relations with the inner orbital cavity. Of the development of the recessus I have no knowledge; but if it is ever connected with the conjunctival region, the position of the organ of the upper orbit shows that this connection must be lost at a very early period prior to the migration of the eye. If a gland at all, it is destitute of glandular epithelium, or, at all events, I have failed to find any. It is, of course, equally possible that a gland might in process of evolution take on new functions and lose its glandular nature, or that a non-glandular ancestral structure might become specialized for a glandular function; but, in the absence of any information as to the origin of the lacrymal gland of higher animals, speculation on this point is more or less idle. From what we have seen of the anatomy of the recessus in its fully developed condition, it appears to m e most reasonable to regard it merely as a part of the ordinary membranous wTall of the orbital cavity, specialized to perform certain definite functions in connection with the elevation of the orbit, and not homologous with any organ known to exist in the eye-apparatus of higher animals, and I have been guided by this opinion in m y choice of a name. It m a y probably occur rather widely in Telosteans which have the habit of burying themselves in the sand. Of such forms I have only examined Trachinus draco and T. vipera, in both cases with negative results. In conclusion, m y thanks are due to m y friend and teacher, Professor Howes, for many valuable suggestions. 1 Cf. Kolliker, Entwick. des Mensch., Leipzig, 1879, p. 699. I am indebted to m y friend Mr. M . F. Woodward for this and other references bearing on the same subject. |