560 LOCY. [Vol. XI. 



has recently come more evidence bearing in the same direc- 

 tion. This consists in the discovery of multiple pineal eyes, in 

 several distinct forms, and, in one case, the existence of three 

 distinct nerves to the pineal organs (see section on The Pineal 

 Sense-Organs). 



Whitman, in his paper just cited, says : " Although the 

 evidence appears to me conclusive that the eyes and the 

 segmental papillae were, originally, morphological as well as 

 physiological equivalents, it does not, of course, follow neces- 

 sarily that both organs now have the same functional signifi- 

 cance. The original papillae may have represented sense-organs 

 of a more or less indifferent order, among which, in the course 

 of the historical development of the leech, a division of labor 

 was introduced, a few at the anterior end becoming specialized 

 as light-perceiving organs, the rest either remaining in their 

 early indifferent condition or becoming specialized in some 

 other direction. 



"The discovery that these papillae are sense-organs might 

 lead us to speculate on affinities of a distant and somewhat 

 uncertain nature, such as are supposed by the writer, in 

 common with many others, to exist between annelid worms 

 and Vertebrates. At all events, the existence of such organs 

 in the leech furnishes a broader basis for the discussion of the 

 question whether the Vertebrates and Annelids have been 

 derived from a common form possessing metameric sense- 

 organs, as was first argued by Dr. Eisig of the Naples Station. 

 Assuming that the sense-organs of the Vertebrate and the 

 segmental papillae of the leech may be traced to a common 

 origin in some remote ancestral form, it does not follow that 

 they should now present close structural resemblances. It is 

 far more important to show that they possess certain general 

 features in common. The most important of their common 

 features is undoubtedly their metameric origin. The nerve- 

 supply forms another feature of fundamental importance, in 

 which, according to the interesting observations of Mr. Beard, 

 on the segmental sense-organs of the lateral line {Zool. 

 Anz.y VII, Nos. 161 and 162) of the Vertebrate there is 

 essential agreement. The developmental history of these 



