278 W. J. Crozibr, 



nected by processes with the fibers of the integumentary nerves, 

 and through them are brought into relation with the epidermal sense 

 cells. I therefore believe that the yellow pigment of Holothuria 

 is concerned with photo-reception. 



V. Heat. 



1. Introduction. 



H. surinamensis is normally subjected to temperature variations 

 of considerable amplitude occurring within relatively brief time inter- 

 vals (see p. 7). It might reasonably be expected that this condition 

 would be reflected in the behavior of Holothuria toward heat and 

 heat changes. The average temperature of the sea water in which 

 Holothuria was found was 28''. In connection with each laboratory 

 experiment the temperatures of the water in aquaria in which ani- 

 mals were under observation was recorded; the mean of these tem- 

 peratures was 21^, with a range of 22—28,5"; holothurians lived 

 under these laboratory and temperature conditions for variable periods 

 of two weeks and more. 



In studying the effects of heat and of temperature changes on 

 Holothuria, preliminary tests were made to show the influence of 

 high and low temperatures, after which an attempt was made to 

 discover the delicacy of the temperature sense. 



2. Effects of altering the temperature, 



Holothurians placed in beakers of sea water slowly heated on 

 a sand bath were observed in ten experiments. The temperature 

 was raised from 27° to 45° at the approximately constant rate of 

 1° in four minutes. Table X contains the condensed notes of these 

 experiments. 



Table X. 

 Exp. 49. 



Temp. Notes. 



27° Laboratory temperature at beginning of experiment. 



29° Tentacles contracted frequently. , 



QAO f Considerable longitudinal contraction of the body. 



\Tube feet loosened from the bottom in most cases. 



3 1 ° ^ 



o^of Shadow response gradually destroyed (see page 39). 



