176 CARNEGIE INSTITUTION OF WASHINGTON. 



most resistant to increased temperature occupy the most exposed and shallow- 

 est portions of the reefs. The species most affected by increase in temper- 

 ature are deeper-water forms not usually found on shallow reefs, in tide-pools, 

 or where there is much sediment on the bottom. The distribution of the 

 Alcyonaria on the reefs about the Sam.oan Islands was also found to be in 

 accord with their powers of resistance to increased temperature. 



When studied in reference to their heat resistance, the 12 most abundant 

 species of Alcyonaria about Tortugas fall into several well-defined groups. 

 Pseudoplexaura crassa and Eunecia crassa are unable to withstand a tempera- 

 ture of 34.5° C. for 1 hour; Plexaura flexuosa, P. homomalla, Plexaurella 

 dichotoma, Plexaurella sp., Eunecia rousseaui, and Muricia muricata were killed 

 by an exposure to a temperature of 35° C. for 1 hour; Gorgonia flahellum and 

 G. acerosa were lulled by exposure to 37° C. for 1 hour; Gorgonia citrina and 

 Xiphigorgia anceps survive all temperatures up to 37.5° C; while Briareum 

 ashestum was not killed until a temperature of 38.2° C. was maintained for 1 

 hour. The temperature range of the Alcyonaria is thus practically identical 

 with that of the Madreporaria. 



On the shallowest portions of some of the reefs about Tortugas the temper- 

 ature of the water during the hottest days in summer, when low tide comes 

 late in the afternoon, frequently rises to that which is fatal to all of the Alcyo- 

 naria studied. On any reef where there is an active circulation of water the 

 temperature has never been observed to reach that fatal to the least-resistant 

 species for periods of sufficient length to cause their death. The temperature 

 effect is therefore of very narrow application on the reefs about Tortugas. 

 Even when, as sometimes happens, the distal portions of alcyonarian colonies 

 are exposed to the air for a considerable time, it is seldom fatal to the species 

 having a loose-tissue structure. On some of the shallowest reefs mature speci- 

 mens of none but the most resistant species are found, while small specimens 

 of the less resistant forms are sometimes abundant, but in other seasons are 

 almost entirely absent. These facts may perhaps be accounted for by the 

 destruction of the less resistant species because of the high temperature of the 

 water, although other factors can not be excluded when these reefs are visited 

 at intervals of a year and at practically the same season each time. 



The oxygen consumption of colonies of the same species was found to be 

 directly proportional to the mass of living tissues in a colony and to vary 

 only slightly with the physiological state of the specimen. A colony in which 

 each polyp was in full expansion did not respire any more rapidly than did 

 the same colony when its polyps were kept withdrawn within the coenenchyma 

 because of the rotation of the jar within which the experiment was being 

 carried out. 



The oxygen consumption per gram of living tissue per hour varies for dif- 

 ferent species from 0.0139912 c.c. {Briareum ashestum) to 0.07459 c.c. (Gorgonia 

 flahellum). There was found no apparent correlation between the activity of 

 metabolism and resistance to heat. The least-resistant forms have an inter- 

 mediate respiration-rate; the most-resistant species has a very low respiration- 

 rate; while the species of the genus Gorgonia, which constitute a group of highly 

 resistant forms, have the most rapid metabolism. Although there was no 

 constant difference in the respiration of the same specimen when its polyps 

 were contracted or expanded, in spite of the fact that in the last-named condi- 

 tion the surface area was increased to 1.5 times that of the former, a high respi- 

 ration-rate was observed in all those species in which the area was greatest in 

 proportion to the mass of the colony. The relation between the values of 

 the constant a/w (area divided by the weight) for the several species was prac- 



