Seusory reactions of Holothuria surinameiisis. 237 



the muscles are composed of unstriated spindle cells, which show a 

 faint longitudinal fibrillation (Hamann, 1883, Geeould, 1896). Their 

 physiology (in Holothuria) has to some extent been studied by 

 Biedermann (1889). From the fact that the musculature of Holo- 

 ihuria is made up of nonstriated cells, it must not however be 

 inferred that it is physiologically comparable to the nonstriated 

 contractile tissue of vertebrates. The experiments of v. üexicüll 

 (1896) and others show that, in general, the skeletal muscles of 

 invertebrates (as contrasted with the visceral musculature) contract 

 rapidly in response to a variety of stimuli, as do the skeletal muscles 

 of vertebrates. 



The manner in which the muscles are concerned in the body 

 movements of Holothuria has been discussed at length by Hérouard 

 (1889, pp. 592 et seq.), and in many text books. The essential 

 point is that the muscles work upon the incompressible fiuids of 

 the body cavity. After being contracted, the body is re-extended 

 by the relaxation of the musculature and the pumping in of water. 



The sense organs and the conducting portion of the nervous 

 system will be considered in the discussion of the experimental 

 results. H surinamensis is not a "cotton-spinner". The Cuvierian 

 ■organs are found in only a few individuals, and even then but 

 poorly developed. H. captiva, however, discharges its sticky "cotton" 

 on the slightest provocation; Clark (1901c, p. 257) notes that in 

 this species the Cuvierian organs may amount to as much as one 

 tenth of the total bulk of the individual. 



2. Habitat and activities. 



' The life of Holothuria in its normal habitat was studied with 

 the purpose of obtaining a proper background on which to view 

 the results of laboratory experiments. 



a) Habitat. According to Carpenter (quoted by Clark, 1899, 

 p. 122) H. surinamensis "can be picked up almost anywhere along 

 the reef protected shore . . . among broken rocks", and Verrill (1906, 

 p. 278) states that it also occurs on the reefs. While specimens 

 were found in such situations, they were much more plentiful, near 

 the Agar's Island Station, in certain sheltered shallow baj'S where the 

 toottom, formed of a considerable thickness of rather loose mud, was 

 covered with masses of matted seaweeds ^) and sponges. The holo- 



1) Most prominent among the water plants were species of Penicillus, 



