126 REPORTS ON INVESTIGATIONS AND PROJECTS. 



object being to throw light on a possible relation between the degree of ioni- 

 zation and reaction. These curves are remarkably regular and show that 

 the rate of transmission of the nervous impulse which produces pulsation 

 varies as does the degree of dissociation of the ions of the sea-water above 

 or below the normal. For stimulating cations this ratio is direct, but for 

 inhibiting cations such as Mg it is inverse. In another research the Director 

 determined the temperature limits of various marine animals, especially the 

 reef corals. The reef corals can not long withstand intense heat, a water 

 temperature of 99 ° F. being fatal to most of the species. Siderastrea radians 

 is most resistant to temperature changes, its life-limits ranging from about 

 42 ° to 101 F. ; and one specimen survived with some maceration after being 

 11 hours in the ice-box, the final temperature of the water surrounding it 

 being 35.4 F. It is difficult to see why this coral does not range much 

 farther north than the other reef corals. The most sensitive of the reef- 

 building forms appears to be Orbicella annularis, whose life-limits are be- 

 tween 58 ° and 97. 5 F. 



We have record of a northerly storm in the winter of 1911-12 which 

 cooled the water in the moat at Fort Jefferson to 63 ° F. In view of this, 

 I maintained various reef-corals at a water-temperature of as nearly as 

 possible 57 F. for 9 hours, and then returned them to the ocean, which was 

 at its normal summer temperature of about 82.5 ° F. As a result of these 

 experiments I am led to conclude that were the sea-water surrounding the 

 corals to be cooled to 57 ° for 9 hours Siderastrea radians, S. siderea, and 

 Mceandra areolata would survive without apparent injury, while Porites 

 furcata, Mceandra clivosa, Porites clavaria, and Favia fragum would prob- 

 ably survive with more or less maceration of tissue, the first named being 

 the hardiest. On the other hand, Orbicella annularis, Porites astreoides, and 

 Acropora (Madrepora) cervicomis would be killed. In general, the shal- 

 lower and the more stagnant the water in which the coral normally lives, 

 the more able it is to withstand high or low temperatures. 



Relatively deep water forms, such as Eusmilia knorri and Oculina diffusa, 

 are not so resistant to heat as the reef-builders, being killed at 97 F. ; but 

 on the other hand they withstand cold quite as well if not better than most 

 of the shallow-water forms. 



In common with other tropical marine creatures, the corals live in an 

 environment which is much closer to their death temperatures than that 

 of northern animals. One may contrast the behavior of the most resistant 

 coral, Siderastrea radians, which can survive between 101 and 42 F. and 

 which lives in water ranging between 92 and 63 F., with some such form 

 as Limulus, which ranges from Maine to Yucatan and survives between 

 110 and — 2. 75 , being able to withstand being frozen into the ice. 



In another research the Director continued the study of the rate of star- 

 vation of Cassiopea xamachana in sea-water sterilized in various ways, the 

 animals being either normal or regenerating, or in light or in darkness. It 



