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Notes on the Life History of Gammarus cheureuxi 



By 

 E. W. Sexton and Annie Matthews, M.Sc. 



INTKODUGTIOK 



The present paper is the outcome of an investigation made on a 

 species of Gammarus inhabiting both fresh and brackish water 

 (4, p. 657). As this species {G. zaddachi) seemed to show a marked 

 variation in appearance according to its environment, we instituted 

 experiments in the Laboratory at Plymouth on G. chevrcuxi to see if a 

 similar variation in appearance could be brought about by varying the 

 degree of salinity of the water in which the animals lived. 



It would have been impossible to have obtained any measure of 

 success without the kind co-operation of Dr. Allen, and we wish here 

 to acknowledge our indebtedness to him, and to the various members of 

 the staff for their continual and willing help. 



Our ultimate object, which is to establish if possible a variation in 

 the appearance of a given species by altering its environment, has had 

 to stand over for a time, until other more pressing problems were 

 settled. The first of these was how to ensure a constant supply of 

 healthy animals, able to live and breed under Laboratory conditions, 

 and the next was to find if it were possible to bring them to live in 

 fresh water and in sea-water. In both of these experiments we 

 have succeeded far better than we anticipated. We have now 

 (January, 1913) the young of the fifth generation, bred from the 

 animals captured in June ; and, after some three months' gradual 

 altering of the original water, we have some individuals living and 

 breeding in absolutely fresh water, while others of the same stock are 

 living and breeding in pure sea-water. Other problems in the life 

 history have still to be worked out, this paper being intended only as 

 a summary of the work as far as we have gone. Some of our conclu- 

 sions will no doubt need revision later. 



It must be remembered that the results here given are all obtained 

 under artificial conditions. If it were simply a question of multiplying 

 generations the conditions could have been made more like the natural 



