SEA- FISHERIES LABORATORY. Ill 



will be seen that the right eye is quite normal, whereas 

 the left orbit is covered over by skin and has a little raised 

 part at its centre. It was expected that something 

 interesting might be disclosed on a more minute investi- 

 gation, so a series of sections through the orbital region 

 were made. One of these sections passing nearly through 

 the centre of the right eye is represented in Text-fig. 7. 



Both eyes ought to appear, nearly meridionally, in 

 the same section. The left eye is, however, wanting, and 

 the connective tissue which lies immediately underneath 

 the integument occupies very much the position which 

 would have been that of the sclera of the left eye had it 

 been present. The eye-muscles are present, and are 

 nearly normal in their development. The ophthalmic 

 artery (that is, the efferent pseudobranchial vessel, or the 

 afferent vessel of the choroidal gland) is also present, with 

 its vein. The optic nerve is present, although it is 

 greatly reduced distally. In a transverse section of a 

 normal plaice having the plane of that of Text-fig. 7, both 

 optic nerves should have nearly the same area of cross 

 section. Further back than the plane of section of Text- 

 fig. 7 the eye-muscles and nerves of both sides 

 approach each other and enter the common eye-muscle 

 canal together, precisely as in the case of a normal fish. 

 Tracing the eye-muscles and other structures forward in 

 the series of sections, they are seen to die out. They end 

 in the mass of fibrous connective tissue shown in the figure 

 just dorsal to the muscles. The ophthalmic vessels become 

 occluded and disappear from the sections in the same 

 tissue. 



The integument lining the orbit of the missing eye 

 is modified. It becomes very much thicker, and there is 

 a great development of sub-epidermal fibrous tissue (not a 

 real corium). The epidermis contains very numerous 



H 



