ii CHROMATOPHORES 243 



and is hence fluorescent-, when examined through the 

 spectroscope it has the effect of absorbing the whole of the 

 blue 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 hccmatocJiroine. 



At first sight the chlorophyll appears to be evenly distri- 

 buted over the whole body, but accurate examination under 

 a high power show r s it to be lodged in a variable number 

 of irregular structures called chromatophores (Fig. 68, A, chr\ 

 which together form a layer immediately beneath the 

 surface. Each chromatophore consists of a protoplasmic 

 substance impregnated with chlorophyll. 



After solution of the chlorophyll with alcohol a nucleus 

 (B, mi) 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 structures (A, pyr\ 

 with clearly defined outlines, occurring in varying numbers 

 in the chromatophores. 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 charac- 

 teristic test of the carbohydrate 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 

 pyrenoids. 



In SpJmrella pluvialis there is no contractile vacuole, 

 but in another species, . lacustris, this structure is present 

 as a minute space near the anterior or pointed end (Fig. 68, 

 E, c. vac}. 



R 2 



