78 H. C. SORBY. 



instance ; and in applying it to less known facts, I think I 

 may claim high probability in favour of the provisional con- 

 clusions. It would indeed be premature to look upon the 

 results as more than provisional, seeing that the whole sub- 

 ject is in its infancy. 



At the present time it would be impossible to give a more 

 striking illustratio^ of this method of research than the 

 various facts which seem to indicate the gradual evolution of 

 haemoglobin. Very much remains to be learned, and I now 

 publish what I have so far been able to learn, chiefly with 

 the view of attracting attention to a most promising field for 

 research, and to show the importance of the spectrum 

 method in the investigation of the comparative physiology of 

 the lower animals. 



Some few months ago I commenced the study of the 

 different coloured substances found in the shells and soft 

 parts of various species of Mollusca. Many of these have 

 very striking characters, but on the present occasion I shall 

 confine my remarks almost entirely to those which bear on 

 the evolution of haemoglobin. 



If the common large snail, Helix aspersa, kept some time 

 without food in autumn, be killed with chloroform and then 

 immediately dissected, it will be found that the intestine 

 near to the part where the secretion from the liver passes 

 into it, is more or less distended by a reddish-brown liquid, 

 which easily runs out when the intestine is cut. There 

 cannot, I think, be any doubt that this bile is a mixture of 

 at least two coloured substances. One is probably related 

 to the brown substance, quite unlike the chief coloured con- 

 stituent of the bile of the higher vertebrata, which is the 

 cause of the dark colour of the liver, especially in Helioe 

 nemoralis, and gives no well-marked or characteristic 

 spectrum. The other gives one very dark and well-defined 

 absorption-band towards the yellow end of the green, and 

 another much more faint towards the blue end of the green. 

 That this substance is not a product of decomposition is 

 proved by the fact that the bands can be well seen in light 

 transmitted through a living Limax. At first sight the 

 spectrum might easily be mistaken for that of deoxidized 

 hsematin, but on comparing them together side by side, 

 though the bands of this bile pigment are of exactly the 

 same character as those of the deoxidized hsematin from 

 human blood, they are in a most decidedly different position. 

 There is, in fact, the same kind of relation between these 

 two spectra as that between the spectra of haemoglobin when 

 loosely combined with different gases. This bile pigment. 



