n CHROMATOPHORES 243 



under a strong reflected light, and is hence fluorescent ; 

 when examined through the spectroscope ic has the 

 effect of absorbing the whole of the clue and violet end 

 of the spectrum as well as a part of the red. The red 

 colour which occurs in so many individuals, sometimes 

 entirely replacing the green, is due to a colouring matter 

 closely allied in its properties to chlorophyll, and called 

 h&fnatochrome. 



At first sight the chlorophyll appears to be evenly 

 distributed over the whole body, but accurate examina- 

 tion under a high power shows it to be lodged in a 

 structure called a chromatophore (Fig. 68, A, chr), which 

 forms a layer immediately beneath the surface, and in 

 this case is relatively large and urn-shaped. It 

 consists of a protoplasmic substance impregnated with 

 chlorophyll. 



After solution of the chlorophyll with alcohol a nucleus 

 (B, nu) can be made out ; like the nucleus of Amoeba, it 

 is rendered more distinct by staining. Other bodies 

 which might easily be mistaken for nuclei are also visible 

 in the living organism. These are small ovoidal struc- 

 tures (A, pyr), with clearly defined outlines, occurring in 

 varying numbers in the chromatophore. When treated 

 with iodine they assume a deep, apparently black, but 

 really dark blue colour. The assumption of a blue 

 colour with iodine is the characteristic test of the carbo- 

 hydrate starch (p. 72), as can be seen by letting a few 

 drops of a weak solution of iodine fall upon some 

 ordinary washing starch. The bodies in question have 

 been found to consist of a proteid substance covered 

 with a layer of starch, and are called pyrenaids. 



In S. pluvialis a distinct contractile vacuole is wanting, 

 but in another species, S. lacustris, this structure can 

 be recognised as a minute space near the anterior or 

 pointed end (Fig. 68, E, c. vac). 



R 2 



