458 E. EAY LANKESTKR. 



From the specimens received in Oxford, after examination of 

 the histological relations of the pigment, Dr. Benham prepared 

 an alcoholic solution which we proceeded to study by means of 

 the spectroscope, and the application of acids and alkalies. A 

 portion of the pigment in aleoliolic solution was sent by nie in 

 the spring of 1897 to Professor Engelmann, together with the 

 solution of Chsetopterin. I am thus able to give here a very 

 accurate record of the absorption spectra of Bonellin (Plate 37), 

 for the purpose of comparison with those of Chsetopterin. It 

 will be seen at once that the two bodies differ entirely from 

 one another in colour and absorption phenomena, whilst 

 agreeing in solubility, fluorescence, and in the exhibition of 

 neutral, acid, and alkaline conditions. 



The appearance of the absorption bands of alkaline and 

 acidulated alcoholic solutions of Bonellin, as seen with the 

 Sorby-Brovvning micro-spectroscope, are drawn by Dr. Benham 

 in Plate 35, fig. 5. The freshly prepared solution of Bonellin 

 is alkaline, of a deep chrome-green colour. It is in this condi- 

 tion that the pigment appears to exist in the skin of the 

 animal (Plate 35, fig. 11). When neutralised the solution 

 assumes a greyish-blue colour (Plate 35, fig. 9). The addition 

 of a small quantity of acid to the neutral solution, changes 

 the colour to a splendid violet (Plate 35, fig. 10). The ab- 

 sorption spectra of these three conditions of Bonellin have 

 been described by Sorby and after him by Krukenberg and 

 by Schenck (who erroneously regarded Bonellin as a form of 

 chlorophyll). 



It will be found that the statements of these authors (cited 

 on p. 449) are at variance in minor details with one another, 

 and also with what I now place on record as the result of the 

 observations of Professor Engelmann. 



The carefully neutralised alcoholic solution of Bonellin 

 exhibits but four marked or isolated maxima of absorption 

 (absorption bands), as shown by Professor Engelrnann's chart 

 (Plate 37). These are as different in position as they well can be 

 from the four bands of Chsetopterin. There is no need to refer 

 any further to a possible relationship between these two bodies. 



