THE LAW GOVERNING THE LOSS OF WEIGHT IN STARVING CASSIOPEA. 



By Alfred Goldsborough Mayer. 



METHODS. 



Before being weighed each medusa was dried upon filter paper so as to 

 remove the water adherent to its surface. It was then weighed in 25 c.c. 

 of sea-water on a delicate balance, the weight of the medusa being deter- 

 mined by subtracting the weight of the water and the glass beaker serving 

 as its container. 



The medusae were starved in sea-water which had been passed through 

 two glass funnels, each containing a double layer of the best quality of 

 Chardin's filter paper, thus removing the zooplankton upon which Cassiopea 

 feeds. In some of the experiments the sea-water after having been passed 

 through Chardin's filters was refiltered through porcelain or it was rendered 

 sterile in so far as animal life was concerned by heating it to 71 C. and 

 then restoring the evaporation by distilled water. These additional pre- 

 cautions were, however, found to be unnecessary for the Chardin filters 

 removed all or practically all food from the water. 



The medusae were always starved in the purest sea-water which was 

 either dipped from the ocean in glass or canvas buckets or pumped into 

 glass reservoir tanks through hard-rubber pipes by means of a hard-rubber 

 pump. In running comparative series care was taken that the sea-water 

 in which each medusa was starved had had the same history; i. e., was 

 gathered in the same way, stored in the same tank, etc., for every medusa 

 in the series. Whenever possible the medusae were starved side by side in 

 one and the same glass aquarium, but when this was impossible the aquaria 

 were of similar size and form and were placed side by side, so as to be sub- 

 jected to similar environmental changes. 



EXPERIMENTS. 



It is a pleasure to acknowledge my indebtedness to Dr. Francis Gano 

 Benedict for important advice and highly appreciated kindness, and to 

 Mr. Joseph C. Bock, of the Nutrition Laboratory of the Carnegie Institution 

 of Washington, for having determined the nitrogen content of the medusae. 



In common with other scyphomedusae, Cassiopea xamachana consists of 

 a large central mass of gelatinous substance, which is covered with a thin 

 layer of cellular tissue, the weight of the gelatinous substance being very 

 great in proportion to that of the cellular elements of the medusa's body. 



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