1899.] NATURAL SCIENCES OF PHILADELPHIA. 141 



aud its surroundiugs is farther enhanced by its pigmented surface 

 which favors both radiation and absorption of heat. In being 

 thus adapted to a bodily temperature very near to that of the 

 minimum for protoplasmic activity, this worm resembles deep- sea 

 animals. Semper has shown ('81) that it is the mean tempera- 

 ture, and not its fluctuations, which is important in determining 

 the rate of growth of an animal; and here Ave have an organism 

 whose optimum temperature has probably been adjusted to a point 

 at which metabolism ceases in most other animals. Nothing is 

 known of the winter habits of the worm, but no doubt it burrows 

 deeply into the snow, and thus protected, lives in an environment 

 the temperature of which probably varies little from that of its 

 summer habitat at the surface. 



But little is known as yet of the geographical distribution of the 

 Enchytraeidse. They have been described from Europe, Asia, North 

 and South America, Greenland and New Zealand. But it is only 

 in Europe that our knowledge of the species and their distribution 

 is even approximately complete. From what is known of the 

 distribution of the Eurasian species the statement seems to be war- 

 ranted that this family reaches its greatest development in the 

 colder regions. Species abound in Siberia, NovaZembla, Denmark 

 and Norway, and some are found in Spitzbergen and Greenland, 

 where other Oligochieta are very rare. Very few species have as 

 yet been described from the American continent, but, so far'as our 

 information goes, it confirms the results of a study of the distribu- 

 tion of the Old World forms. The tropical and subtropical 

 forms appear to be few and small, while many have been described 

 by Michaelsen ('88") and Ude ('96) from the southern extremity 

 of South America. They abound and present much variety in the 

 northern United States, though but comparatively few species have 

 been described. What is stated for the family seems to be preem- 

 inently true of the genus Mesenchytrceus. Of the eleven species 

 recorded for Eurasia, none have been reported south of Germany, 

 where Michaelsen ('89) has found and described three species; three 

 species are also found each in Siberia (Eisen, '79), Nova Zembla 

 (Eisen, '79, and Levinsen, '83) and Denmark (Levinsen, '83). 

 None have been reported from North America, but two species, one 

 of which is probably M. beaumeri Mich., and the other unde- 

 scribed, occur in the neighborhood of Philadelphia. Ude men- 



