Sensory reactions of Holothuria surinamensis. 281 



6. 41 — 45^. Coagulation of the muscle substances and consequent 



death. "Heat rigor" is either totally absent, or 

 passes very quickly. 



7. The tentacles (especially) respond to currents of water 



at temperatures differing widely from the normal. 



Matee (1911, p. 125) found, that, to have an animal survive in 

 the shallow or surface waters of the tropics, it must be able to 

 withstand a temperature of 29** C. Most of the more highly orga- 

 nized marine forms are capable of doing this, for (Veknon, 1899, at 

 Naples) their death temperatures when subjected to experimental 

 heating are in the neighborhood of 40*^. Paekee (1908) found the 

 temperature producing death by coagulation to be about 40** in the 

 case of the Bermuda Amphioxus. The behavior of Holothuria as it 

 was gradually heated is characteristic of many other marine in- 

 vertebrates, its muscle substances coagulating at about 42**, while a 

 temperature of 45'^ produces almost instantaneous whitening. The 

 maximum temperatures observed in its habitat (31,8") were therefore 

 well within the safety zone. The lethal temperature for some other 

 littoral Bermuda animals would appear to be much nearer their 

 customary thermal condition; the small translucent crustacean 

 Sijnalpheus (inhabiting sponges), for example, was found to have its 

 muscle proteins coagulated when slowly heated up to 37°, a tempe- 

 rature of only 34° causing them to become immobile. 



It seems quite clear that there is no well developed capacity 

 for the reception of thermal stimuli. Such reactions as were ob- 

 tained to currents of warm sea water, directed on to the tentacles 

 are more properly interpreted as due to the lowering of the thresh- 

 old to mechanical stimuli at the higher temperatures. Thyone, 

 also, is "comparatively insensitive to thermic changes" (Peaese, 

 1908, p. 281). 



VI. Chemical stimuli. 



1. Introduction. 



No quantitative analysis of the chemical sense in echinoderms 

 has thus far been made. The experiments of Romanes (1885), 

 Peetee (1886), Peouho (1890), Nagel (1894), Jennings (1907), 

 V. Uexküll (1905), and others who have studied starfishes and 

 sea urchins have demonstrated that there is present a chemical 

 sense of the general nature of smell (i. e,, a distance receptor), and 



19* 



