DEPARTMENT OF MARINE BIOLOGY. 185 



The idea that the prevaiUng temperature at Tortugas is so high that heat- 

 blanching would necessarily follow and the possibility of adaptive reaction be 

 limited thereby, is due to a misconception of the facts. A thermometer lying 

 on the sand, say 25 feet above high-water mark, will frequently record a 

 temperature above 45° C. It is not, however, in that zone that the crabs are 

 to be observed, but much lower upon the beach. Moreover, their bodies are 

 not on the sand, but above it. If one uses the thermometer with these facts 

 in mind, the case assumes an entirely different aspect. 



At 2'45'" p. m. on August 10, 1917, the temperature recorded by a thermom- 

 eter lying on the sand about 25 feet above high-water mark on the beach at 

 Tortugas was 49° C. When the instrument was elevated half an inch upon 

 two crotched sticks the mercury fell to 40° C. In the middle of the exposed 

 zone below high-water mark the corresponding temperatures were 39° C. 

 and 37° C. respectively. The latter is at the most not more than 2° above the 

 point where on the average heat-blanching becomes evident. Up and down 

 the whole length of the beach, where earlier or later in the day large numbers of 

 the creatures might be seen feeding or running actively about, only 5 were 

 visible when these observations were made. These were all digging or lying 

 in the mouths of their burrows. Hence it is apparent that the range of Ocy- 

 poda is so restricted and that its activities vary to such an extent during the 

 day that when and where it freely exposes itself there is no known factor 

 which necessarily limits its theoretically advantageous color adjustments. 



The facts established concerning the color-changes of Brachyura show 

 among other things how closely a creature's habitat must sometimes be de- 

 fined before there is any possibility of comprehending its degree of adaptation 

 to its environment. In view of what has been learned regarding the colora- 

 tion of fishes^ they are particularly significant, however, because of their sug- 

 gestion that the coloration of crabs conforms to the same general laws. 



On the Non-Existence of Nervous Shell-Shock in Fishes and Marine 

 Invertebrates, by Alfred Goldsborough Mayer. 



Experiments made at Tortugas during the summer of 1917 indicate that the 

 nervous systems of fishes and invertebrates are remarkably resistant to the 

 injurious effects of sudden explosive shocks. Many experiments were made 

 upon the Scyphomedusa Cassiopea xamachana. The medusae were paralyzed 

 by removing their marginal sense-organs, and then a ring-shaped strip of sub- 

 umbrella tissue was set into pulsation by an induction shock, thus producing 

 a single neurogenic contraction which travels through the circuit-shaped strip 

 of tissue at a uniform rate of speed, provided temperature, salinity, and other 

 factors remain unchanged. It is thus possible accurately to ascertain not 

 only the rate of nerve-conduction, but also the peculiar individual character- 

 istics of the wave in each pulsating ring. 



These rings were placed in a light silken bag immersed about 10 feet below 

 the surface of the sea and a half stick of dynamite was exploded within 3 feet 

 of them. This, however, produced no effect, either upon their rates or the 

 character of their pulsation waves, although fishes possessing swim-bladders 

 were killed within 10 feet, and wdthin 20 feet of the exploding dynamite were 

 injured so that they turned ventral side uppermost. 



When the pulsating rings were placed in glass jars or tin cans, partly filled 

 with ail', the containers were crushed or shattered by the explosion and much 



'Longley, W. H. : Studies upon the biological significance of animal coloration: I. The colors 

 and color changes of West Indian reef-fishes. Jour. Exp. Zool., vol. 23, pp. 536-601 (1917). 



