4 Papers from the Marine Biological Laboratory at Tortugas. 



general truth; for example, Professor Hjort, in Murray and Hjort's "Depths 

 of the Ocean" (1912, p. 444), concludes that the southern limit of northern 

 boreal species of fishes from the sea-bottom everywhere coincides with the 

 isotherm of 10 C. at a depth of 100 meters. 



That temperature should be so important a barrier to universal distri- 

 bution is the more remarkable in view of the large number of observations 

 showing how readily animals may become artificially adapted to survive 

 in unaccustomed temperatures. Thus Davenport and Castle (1895) found 

 that tadpoles reared at about 15 C. go into heat-rigor at 40 to 41 C, but 

 if kept at about 24.5 C. for 4 weeks their heat-rigor temperature is raised 

 to 43 to 43.8 C. 



The experiments of Dallinger (1887) are even more remarkable, for he 

 kept Flagellata in a warm atmosphere beginning at 15.6 C, gradually 

 raising the temperature for several years until it became 70 C, the colony 

 still surviving and reproducing normally, although in nature the same 

 species were killed at 23 C. 



In studying animals in a state of nature, Vernon (1899) found that at 

 Naples the mean death-temperatures of various marine invertebrates ranged 

 from 34 to 42.3 C, but that the death-temperatures of the same species 

 in July and August are from 0.6 to 1.3 C. higher than in March and April, 

 this change being associated with a rise of about 10 in the surface temper- 

 ature of the Mediterranean. Observations of similar purport were made by 

 King (1903) upon the effects of seasonal temperature on the development 

 of toad eggs. 



It is, therefore, somewhat surprising, when we see how readily certain 

 animals may become acclimated in a short time to abnormally high or low 

 temperatures, that whole races of marine organisms are confined within 

 a narrow range of temperature. For example, the rhizostomous scypho- 

 medusa2 are restricted to tropical or warm seas, none of them extending 

 into regions beyond the summer isotherm of 16 C. Also, the species of the 

 genus Cyanea are equally well confined to cold seas, being bounded in their 

 range from either pole by the summer isotherm of 20. On the other hand, 

 Aiirellia aurita is eury thermal, ranging from pole to pole and giving rise 

 to many varieties and local races. 



Among the 440 known species of hydromedusae only one, Solmundella 

 hitentacidata, appears to be eurythermal, living at temperatures ranging 

 from 30 to 1 C. and at depths between 1,500 fathoms and the surface, 

 and even among the widely ranging Siphonophorse, Bigelow (191 1) is able 

 to name only one doubtfully eurythermal species among the 90 known forms. 



A study of the temperature reactions of the only known eurythermal 

 scyphomedusa, Aurellia aurita, is of interest, for it shows that the success 

 of this species in adjusting itself to a wide range of temperature is due to a 

 remarkable ability for acclimatization. Thus, the A iirellia at Halifax, Nova 

 Scotia, ceases to pulsate at 29.4 C, at which temperature it is most active 

 at Tortugas, Florida; and conversely, the Tortugas medusae cease to pulsate 



