TRANSACTIONS OF THE SECTIONS. ]J 



light, the two innermost rings being positive like zircon, and the 

 outermost negative, like calcareous spar. In other cases, especially 

 when the lenses were taken from older animals, four rings were 

 seen, the innermost of which was positive as before, and the rest ne- 

 gative and positive in succession. 



I now placed a lens which gave three rings, in a glass trough con- 

 taining distilled water, and I observed the changeswhich it experienced 

 from day to day. These changes were such as I had not anicipated ; 

 but though I have observed and delineated them under various modi- 

 fications, I shall confine myself at present to the statement of the ge- 

 neral result. There is a black ring between the two positive structures 

 or luminous rings. After some hours' immersion, in distilled water, 

 this black ring becomes brownish, and on the second day after the 

 death of the animal, a faint blue ring of the first order makes its 

 appearance in the middle of it, and its double refraction, as exhibited 

 by its polarized tint, increases from day to day, till the tint reaches 

 the white of the first order. Simidtaneously with this change of 

 colour, the breadth of this new ring gradually increases, encroaching 

 slightly upon the inner positive ring, but considerably upon the 

 second positive ring ; so that the black or neutral ring which sepa- 

 rates the two positive structures, and in the middle of which a new 

 luminous ring is created, divides itself into two black neutral rings, 

 the one advancing outtvards, and diminishing the breadth as well as 

 the intensity of the second series of positive sectors, and the other 

 advancing inwards, and diminishing the breadth and intensity of the 

 inner or central sectors. While these changes are going on, the 

 outer luminous or negative ring advances inwards, encroaching also 

 on the second positive ring. 



Upon examining the character of the new luminous ring, the de- 

 velopment of which has produced all these changes, I found it to be 

 negative, so that at a certain stage of these variations we have a posi- 

 tive and a negative doubly refracting structure succeeding each other 

 alternately, from the centre to the circumference of the lens, such 

 as I have often observed in lenses taken from animals of greater age, 

 and examined immediately after death. 



After this stage of perfect development, when there is a marked 

 symmetry both in the relative size and polarizing intensities of the 

 four series of sectors, the lens begins to break up. The new negative 

 ring encroaches so much on the two positive ones, which it separates, 

 that the outer one is sometimes completely extinguished, while the 

 breadth and tint of the inner sectors are greatly diminished, so that 

 the highest double refraction exists in the newly developed ring. In 

 a day or two this ring also experiences a great change of distinctness 

 and intensity, and the lens commonly bursts on the fifth or sixth day, 

 sometimes in the direction of the septa or lines where its fibres have 

 their origin and termination, and sometimes in other directions. 



In order to give a general idea of the cause of these singular 

 changes, I may state that the capsule which incloses the lens is a 

 highly elastic membrane — that it absorbs distilled water abundantly 



Vol. V. 1836. c 



