DEPARTMENT OF MARINE BIOLOGY. I3I 



how long it is possible for the impulse to move under favorable conditions, 

 because of its bearing on the question of nerve fatigue. The impulse in one 

 ring was conducted for 1 1 days with no appreciable slowing in the rate. The 

 average velocity was 46,472 mm. per minute, or about 67 kilometers per day. 

 At the end of the 1 1 days, when the impulse stopped suddenly, it had traveled 

 ^2)7 kilometers, or 457 miles. 



The muscle tissue fatigued so that after twelve hours the amplitude was 

 very much reduced. Handling the ring in changing water has no effect on 

 the rate of conduction, but the contraction is increased. After 8 days the 

 muscle contraction is hardly visible. On changing the water the impulse is 

 generally slowed after this time. 



During the day the velocity of nerve conduction is greater than during the 

 night. This fact is possibly due to the variation in oxygen supply conditioned 

 by symbiotic algae in the subumbrella tissue. 



Physiological Studies on the Protozoan Parasites of Diadema setosum, 

 by Dr. Merkel H. Jacobs, University of Pennsylvania. 



The object of these experiments was to determine how far, in the case of 

 a number of forms of parasitic protozoa, presumably of different origin, 

 inhabiting the same host, the similarity of their environment has brought 

 about physiological similarity in the parasites. The method employed was 

 to determine and compare the resistance of each of the forms in question to 

 various artificially changed conditions. The protozoa chosen for the purpose 

 were the ciliates parasitic in the alimentary tract of the large black sea- 

 urchin, Diadema setosum. They are comparatively unspecialized forms, 

 which are easy to obtain in large numbers, and are therefore suitable for the 

 beginning of such a study. The writer intends to extend the results obtained 

 by a series of similar experiments on some of the more specialized forms 

 found in other animals. 



The protozoan parasites of Diadema are chiefly ciliates, of which four kinds 

 are by far the most abundant. These four forms are not closely related to 

 each other and differ widely in size and structure. Since apparently none of 

 them have been described or named, they are designated in these experi- 

 ments, for purposes of convenience, by the letters A, B, C, and D. Form B 

 seems to be present in almost, if not quite, lOO per cent of all adult diademas, 

 C in about 75 per cent, D in about 40 per cent, and A in about 33 per cent. 

 The number of individuals present is often very large. The parasites seem 

 to be confined exclusively to the alimentary tract, and are found chiefly in 

 the upper coil of the intestine. Very young diademas do not contain them 

 and slightly older specimens, while sometimes showing forms C and D, and 

 another form not found in the adult (?), do not seem to contain either A 

 or B. None of the forms in question was ever found in sea-water nor in 

 unrelated animals, although a careful search was made for them. In other 

 genera of sea-urchins, however, they may occur in varying numbers. B was 

 found rarely in Toxopneiistes and Bchinometra, and C on a number of occa- 

 sions in Toxopneiistes, while D seems to be present in every adult Toxo- 

 pneustes, which probably is its true host, and rarely in Bchinometra. A was 

 never found outside of Diadema. A number of specimens of Hipponoe were 

 examined for protozoan parasites, without results. 



The experiments made to throw light on the physiological resemblances 

 and differences of the forms in question dealt with the following points: 

 (i) ability of parasites to live outside the body of the host; (2) ability to 



