238 ^- J- Crozier, 



thurians occurred buried in the mud about the steins of water plants anä 

 the roots of mangrove trees, under stones at or just below low water- 

 line, and in small cavities in the aeolian limestone of the shore. 

 In some restricted areas where the holothurians were most frequently- 

 collected, the bottom was exposed for an hour or more at each low 

 tide; during this time the animals burrowed deeply. Occasionally 

 they were observed partially exposed, the anterior end being buried 

 and the respiratory cloacal end appearing above the mud. Early m 

 the morning, before the sun had risen, the holothurians were found 

 lying freely exposed upon the bottom. They slowly disappeared into^ 

 the silt as the day-light became brighter. In the evening, however^ 

 they were not found at the surface — at least up to twelve o'clock — 

 even on dark nights. While I have not sufficient evidence tO' 

 warrant the statement that this emergence from the mud is a daily* 

 occurence, it would seem that H. surinamensis, like the species- 

 described by Daltell (1851, Vol. 1, pp. 49 et seq.) and the holo- 

 thurians observed by many later workers (cf. Semper, 1868, p. 201),. 

 is essentially a nocturnal animal. Perhaps some special combination 

 of tidal and light conditions is necessary to bring the animals to> 

 the surface. When first collected the animals were covered by a. 

 thin layer of fine silt, apparently held by some mucous secretion,, 

 which adhered tightly but could be peeled off in flakes. Thi& 

 covering did not extend to the tentacles, pedicels, or tips of the 

 papillae — possibly because these parts exercise respiratory and 

 sensory functions. The muddy investment gives the holothurians- 

 the exact color of their surroundings, especially when living among 

 rocks. 



b) Temperature range. The range of temperature to which 

 Holothuria is naturally subjected is of considerable magnitude. 

 Surface water in the Bermudas has in summer an average temperature- 

 of 31*^+ (Parkee, 1908, p. 438, and my own observations); it is^ 

 higher in more open areas: 35"+ (81— 84» F , Mark, 1913). A 

 series of temperature readings at different hours of the day and 

 night indicated that the temperature range, in places from which 

 holothurians were taken at the time the observations were made,, 

 was at least 12" — extending from 20" to 31". The chief 

 factor in the production of this temperature variation is the state 



Halimeda, Laurencia, Acetabulum, Polysiphonia, some filamentous forms,, 

 and Zostera. I am indebted to Mr. F. S. COLLINS for these identifications. 



