DEPARTMENT OF MARINE BIOLOGY. 177 



tically the same as that for respiration, showing that some spatial relations 

 between the different tissues is an important factor in determining the rate of 

 metabolism. 



Studies on the Metabolism of Cassiopea, by L. R. Gary. 



In studying the metabolism of Cassiopea the oxygen consumed was deter- 

 mined by Winkler's method. The experimental specimens were kept in jars 

 of known capacity provided with clamped tops fitting on rubber gaskets, so 

 that no interchange of gases was possible. During any experiment the jars 

 were kept in a large tank of sea-water which was covered with a light-tight 

 cover, a precaution due to the presence in the tissues of the medusa of zooxan- 

 thellae which give off oxygen in the presence of sunlight. The temperature of 

 the water did not vary more than 0.1° during the course of any experiment. 



From the structure of the Scyphomedusae it is apparent that the greater 

 part of their respiration must take place through their ectodermal epithelium, 

 since the endodermal epithelium is of relatively small area and the mesogloca 

 but a structureless secretion formed by the activity of the epithelia. More- 

 over, the muscles are entirely of ectodermal origin and the other most active 

 type of cells — the unicellular glands — are most abundant in the ectoderm. 

 The oxygen consumption ought, therefore, to be most closely correlated with 

 the area of ectodermal tissue. The surface area of an entire medusa is espe- 

 cially difficult to calculate, but that of a medusa disk can be determined as 

 the areas of two equal circles — the exumbrella and subumbrella. It was also 

 found that the relation between the diameter and the weight of any disk is 

 represented very closely by the formula d = 328 -^/wT Since the body of a 

 cassiopea is more than 95 per cent sea-water, no correction was made for the 

 amount of water displaced by the specimen. 



As in my earlier studies on the physiology of Cassiopea, it was found that 

 the individual variations in metabolic activity were so great that reliable 

 comparisons could not be made between different individuals. Safe compari- 

 sons could be made only by using the same specimen in several experiments or 

 by using parts of the same individual in any single experiment. 



The oxygen consumption of entire medusse, taking the average of 20 experi- 

 ments with specimens of various sizes, was 0.03896 c.c.per gram per hour; that 

 of the disks after the removal of the mouth-arms and stomachs was for the 

 same specimens 0.04216 c.c. per gram per hour. The average weight of the 

 entire medusse was 79.95 grams; that of the disks 28.05 grams. The actual 

 average oxygen consumption of the entire medusa was 0.972 c.c. per hour; that 

 of the disks 0.41 c.c. per hour. 



In a series of experiments devised to determine the respiration of the dif- 

 ferent tissues of the disk, it was found that taking the respiration of an actively 

 pulsating half-disk as 100, the active muscles used 36.15 parts, the epithelia 

 (and inactive muscles and nerves) 57.48 parts, the nerves and sense organs 1.37 

 parts, and the mesogloea 5 parts. 



That the mesogloea, although making up so much of the bulk of the body, 

 is relatively inactive is also sho\\Ti by the fact that when a comparison is made 

 betw^een the two halves of a disk, one of which has been split horizontally, 

 thus exposing to the water two surfaces of mesogloea nearly equal in extent to 

 the external epithelial areas, the respiration is only slightly increased. 



The epithelium of the exumbrella consumes 60.5 per cent as much oxygen as 

 that of the subumbrella, when the muscles in the latter are inactive. This 

 figure represents, as accurately as it could be determined, the ratio between 

 the weights of the ectodermal cells covering the two surfaces. Excluding 



