DE. COBBOLD THE EYE OF THE COD-EISH. 



149 



which is slightly constricted below. Very soon after the com- 

 mencement of my examinations, oft-repeated, I have observed the 

 twin-cones to alter in shape. The earliest and most constant 

 change simply consists in the swelling ont of the individual halves 

 of the twin-cone, and their approximation to a more perfect oval 

 figure (i). This occurs before or without the addition of any fluid 

 medium to the slide on which they are placed ; and not unfrequently, 

 under precisely the same conditions, we may see minute appen- 

 dages attached to the lower (or outer in relation to the centre of 

 the eyeball) poles of the twin-cone (as represented at c). Fur- 

 ther disintegration will subsequently take place, even though no 

 fluid be added ; but the changes which thus result accidentally, as 

 it were, are not of that uniform and satisfactory character which 

 enable us to give any opinion as to the probable structure, function, 

 and behaviour of the bodies during life. A very different result, 

 however, happens where we are fortunate enough to secure a fresh 

 eye, in which none of the twin-cones have even begun to disinte- 

 grate, and in which, on the addition of water, we may at once ob- 

 serve a series of changes which I believe to be invariable under the 

 same favourable circumstances. The first time I observed these 

 phenomena was at a meeting of the Brighton Microscopical Society, 

 held during the evening of the 6th of December last. On that 

 occasion, and since, I have observed, with more or less complete- 

 ness, the following changes to take place. The addition of cold 

 water causes a general swelling of the twin-cone, such as I have 

 before referred to as occurring without this agent, and at the same 

 time there commences a bulging at the lower poles of the twin- 

 cone, similar in all respects to that figured at c. These changes 

 are, however, more rapid than those described as taking place from 

 disintegration alone, and, what is more important, they are con- 

 tinuously followed by others still more striking and more uniform 

 in character. Thus (as seen at d), each half-cone assumes a 

 distinctly oval figure, at the same time enlarging, swelling out, 

 and making efforts, as it were, to detach itself from its fellow. Co- 

 ordinating with these peculiarities of behaviour, we observe the 

 protrusions at the lower pole of the twin-cone to bulge more and 

 more conspicuously, and in the interior of the sac-like bacillar 

 prolongations thus formed we have distinct evidences of the exist- 

 ence of a filament, which, owing to its very strong refractive 

 power, exhibits a series of dark transverse bands, apparently 

 disposed in a spiral figure. Singular and inexplicable as these 

 phenomena may appear, I entertain no doubt whatever of their 



