374 J. M. D. OLMSTED 



The same results as for KC1 was produced by 1/10 M CaCl 2 , 

 Na acetate, or Na citrate. 



1/10 M NaCl, MgCl 2 , or Na 2 S0 4 gav.e the same results as a 

 current of ordinary sea-water, i.e., were not stimulating. To be 

 more certain that the effects of 1/10 M KCl, CaCl 2 , Na acetate, 

 and Na citrate were not due to currents, a crystal of oxalic 

 acid was held in forceps just over a Synaptula. When the 

 crystal was above the tentacles they were at once drawn in 

 violently; if over any other portion of the body, there occurred 

 deep local constriction, and the whole body posterior to the 

 stimulated region became greatly contracted; if over the ex- 

 treme posterior end, local contraction took place, a shortening 

 of the whole body, and a lashing about of the posterior end. 



Synaptula hydriformis is therefore very sensitive over its 

 entire body to changes in osmotic pressure and to chemical 

 agents, more so at the anterior end, less at the posterior, and still 

 less in the mid-body regions. It responds to the same categories 

 of chemical agents as do the vertebrates (Crozier, '14 a), i.e., 

 acids, salts, sugars (?), alkaloids, alkalis, and anaesthetics. 



6. General discussion 



It cannot, as yet, be stated whether there have been developed 

 in this holothurian separate sense organs for the different classes 

 of chemical stimuli, or indeed for chemical stimuli in general 

 as distinct from tactile stimuli, etc. The former seems highly 

 improbable, and the latter perhaps doubtful. Aside from the 

 eye-spots and the otocysts, only one type of sensory cell has 

 been described in synaptids (Clark, '98, '07; Retzius, '06), 

 namely the usual invertebrate bristle cell terminating at its 

 deep end with a fiber which connects with a nerve net. The 

 presence of such cells in the vertebrate olfactory epithelium 

 has led Parker ('12) to consider this as the primitive type of 

 sense organ carried over from the invertebrates to the verte- 

 brates. Others (Herrick, '08; Sheldon, '09) have considered 

 the free nerve terminations, which serve as the receptors for 

 the common chemical sense in the vertebrates, to be the primi- 



