INTKOIH'CTOHY. 7 



solution of iodine, the blue colour of the starch, which com- 

 bines with the iodine, can be seen under the microscope. 

 The plant thus gets a large proportion of its food by the help of 

 this green chlorophyll. 



It is a fact of very great interest that chlorophyll also occurs 

 in animals : it is a proof of the fundamental identity between 

 animals and plants ; the living matter or protoplasm of both is 

 capable of manufacturing an identical product. As might be 

 expected, chlorophyll in animals performs a perfectly similar 

 function to that which it performs in plants ; this is particularly 

 the case with certain lowly organised worms in which it occurs. 

 There is a small worm belonging to the Turbellaria, which is 

 entirely without an alimentary canal ; it has neither mouth nor 

 stomach. This creature Convoluta Schnitzel lives in sandy 

 pools left by the sea, associated together in masses, which 

 freely expose themselves to the sunlight. Professor Geddes 

 found some years ago that they give off, when thus exposed, 

 bubbles of oxygen gas, which is of course an indication that the 

 green substance is chlorophyll. 



Other Pigments of Physiological Importance. 



Certain sponges are coloured by a substance which was 

 originally described by Wurm under the name of Tetronery- 

 thrin.* This orange red colouring-matter is widely spread 

 in the animal kingdom ; it occurs, for instance, in two groups 

 so widely separated as birds and sponges ; it is very common 

 in sponges, and is believed by Kriikenberg capable of absorbing 

 oxygen and converting it into ozone ; hence it is clearly of 

 great importance as a respiratory pigment, and is analogous 

 in a way to chlorophyll, or perhaps rather to haemoglobin. 

 Like chlorophyll, it is very susceptible to light. 



* It was afterwards red escribed as Zoonerythrin. 



