358 J. M. D. OLMSTED 



conclude that the statocysts are the organs concerned in the 

 orientation of Synaptula hydriformis to gravity. My experi- 

 ments show further, that Synaptula hydriformis does not re- 

 spond to such vibrations as are said to produce a tone when 

 they reach the ear of man. 



3. The effect of light 



a. Historical One of the earliest observers, and probably 

 the first to record physiological experiments on synaptids, was 

 Quatrefages ('42). He tried the effect of light, [sounds] vibra- 

 tions, mechanical and other stimuli upon his Synapta duvernaea 

 (S. inhaerens) and states (p. 29), "Je n'ai pu reconnaitre chez 

 elles la moindre trace de vision, proprement dite, non plus 

 d'audition ou d'odorat." Nevertheless he thought the activity 

 of these synaptas was reduced during the daytime. When he 

 exposed them to the rays of his lamp concentrated by means 

 of a lens, "elles en etaient evidemment incommode esquelle que 

 fut la partie du corps placee au foyer, mais surtout lorsqu'un 

 dirigeait cette lumiere sur les tentacles; on les voyait alors 

 se detourner et quelquesfois se contracter et revenir en partie 

 sur elles meme" (p. 28). His physiological observations were 

 evidently forgotten for some time, for the discussion of sense 

 organs in synaptids became one of merely anatomical relations. 



The first description of the ' eye-spots' of synaptids was given 

 by Muller ('50 b, p. 226; '52, p. 16). Semper ('68, p. 152) 

 concluded that the sense organs which Muller described, the 

 ' Augenflecken' and 'Gehorblasen,' were both somewhat proble- 

 matical. "Ob die von Muller entdeckten Augenflecke der Synap- 

 ten wirklich als Sinnesorgane, analog den mit dem Nervensys- 

 tem in Verbindung stehenden Pigmentflecken verschiedener 

 Thiere, aufzufassen sind, ist noch nicht zu entscheiden." Baur 

 ('64) found that in Synapta digitata the pigment masses which 

 lie at the bases of the tentacles are not different from those 

 scattered over the surface of the body, and Hamann ('84, p. 

 26) agreed with Baur that they should not be considered as 

 'Augenflecke,' but simply as 'Plasmawanderzellen.' Semon 



