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Show 1894.] TELEOSTEAN M O R P H O L O G Y . 423 Common Sole, my attention was arrested by a sac-like structure lying immediately behind the lower eye, external to the membranous wall of the orbital cavity. The absence of any mention of such a structure in Cunningham's monograph of that speciesl suggested that the specimen under examination might be in that respect abnormal; but I have since found it in every Sole which I have examined, and there can be no doubt but that it is a regular feature in the anatomy of the species. The organ in question is almost certainly homologous with a rounded process of the membranous wall of the orbital cavity discovered by Dr. Giinther2 in Chorisochismus dentex, one of the Gobiesocidae, and conjectured by him to represent the saccus lacrgmali" of higher animals. Beyond this I have been able to find no reference to the existence of any structure at all corresponding to that n o w under consideration. It was m y intention, before publishing, to work out the development of tbe organ as completely as possible, since any opinion that might be formed as to the homologies of the structure would be of little value unless supported by a knowledge of its ontogeny. The material at m y command, however, has proved unsuitable for the purpose, and, since some considerable time must elapse before fresh specimens of the required stages are available, I have thought it best to put forward such information as I have already collected, imperfect as it is, in order to attract the attention of others who may find themselves in a position more favourable for the prosecution of the inquiry. I have ventured to apply to the organ the name (Recessus orbi-talis) which appears at the head of this section. Distribution in Species. I have found the organ present, iu some form or another, in every species of flat-fish examined for this purpose, aud believe that it will be found to occur in all. The species examined comprise the Halibut (Hippoglossus vulgaris), Long Bough Dab (Hippo- (/lossoides platessoides), Plaice (Pleuronectes platessa), Flounder (P. flesus), C o m m o n Dab (P. limanda), Lemon " Sole" (P. micro-eephalus), C o m m o n Sole (Solea vulgaris), and Brill (Rhombus Icevis). Topography and Structure. The organ consists usually of a sac-like process of the membranous wall of the orbit, and in all the forms mentioned, except the Halibut, both orbits are furnished with such a process. The condition in the Plaice may be taken as fairly representative of that met with in the genera Pleuronectes, Hippoglossoides, and Solea, so far as their anatomy is known to m e in this respect. 1 'A Treatise on the Common Sole,' Plymouth, 1890. 2 Cat. Fish Brit. Mus. vol. iii. p. 490. 28* |