ABSTRACT AND REVIEW. 101 



cyst contents into energids can be artificially effected hy expo- 

 sure to strong sunlight, when the protoplasm and chroniato- 

 phores are found to have grouped themselves round the 

 individual nuclei, apparently to screen them from excessive 

 light ; and if this treatment be prolonged, many of the chroma- 

 tophores become transformed into first olive-green and then red 

 oil-drops, which always occupy a position outside the energids, 

 where they can shield the nuclei and the remaining chromato- 

 phores from the sun. By still further prolonging this treatment 

 all the chromatophores can be so transformed, but this is 

 followed by the death of the individual. 



These oil-drops are also always most plentifully found in 

 material taken from dry or sunny places, and they are often to 

 be seen, as Geddes observed, between the layers of the cyst, in 

 which case it seems probable that they are rejected by the 

 organism when no longer of any use to it. The red colour of 

 the oil-drops finally changes to a deep brown or black, similar 

 in appearance to the granules of the digested Algae, whence 

 it seems probable that they may be used as food. 



In favourable places the whole cycle of the life history may 

 be repeated several times in a summer. In winter, and in 

 dry or otherwise unfavourable places, the cyst becomes very 

 thick and stratified (Fig. D, 1). 



IV. The Cell Contents. 



a. The Nuclei. — These can only be satisfactorily demon- 

 strated by appropriate fixing and staining reagents, although 

 in the living cysts the clear masses of protoplasm in which the 

 nuclei lie can sometimes be seen if the chromatophores and 

 other cell contents are not too numerous. The calcium oxalate 

 crystals are also a great hindrance to accurate observation, and 

 must, before staining, be got rid of by treatment with hydro- 

 chloric acid. 



The fixing reagents used were absolute alcohol, aqueous 

 picric acid, chromic acid, and various mixtures of these two 

 with acetic and osmic acids. Finally, and most generally^ 



