92 



Nachdruck verboten. 



The Function of the Chiton Subradular Organ. 



By Harold Heath, Leland Stanford Jr. University, California. 

 With 4 Figures. 



The subradular organ of the chitons, situated at the bottom of 

 the subradular sheath formed by the backward prolongation of the 

 hinder wall of the mouth cavity, is a bilobed structure that has aptly 

 been compared to two beans with their concave surfaces in contact. 

 Its outer layer, bounding the mouth cavity, consists of the buccal 

 epithelium modified at this point into high and ciliated columnar cells 

 usually pigmented and differentiated into sense and supporting cells. 

 The remaining portions of the organ consist of numerous muscle and 

 connective tissue fibres that in addition to their other functions afford 

 lodgement for the relatively well developed subradular ganglia. 



Owing to its position and abundant nerve supply this structure 

 has long been considered an organ of special sense. By some it is 

 believed to be tactile in function, others look upon it as gustatory, 

 while a few would combine with one or both of these activities the 

 sense of smell. At the present time it is impossible to say which if 

 any of these views is correct since observations on the living animal 

 are very incomplete. 



A step toward the solution of the problem was made by Thiele x ) 

 who discovered that by the pressure of the blood the subradular organ 

 could be protruded from the mouth. This observation was made on 

 preserved material, however, and since it was not known to be a 

 normal performance its significance was not appreciated. 



More recently Plate 2 ), working on both living and preserved 

 material, has greatly added to our knowledge of the Chitons and has 

 given us additional information concerning the structure and relations 

 of the subradular organ together with its possible use. In the prin- 

 cipal species examined by him, Acanthopleura echinata, this 

 author frequently found that in both living and dead specimens the 



1) J. Thiele ('95), Ueber die Verwandtschaftsbeziehungen der 

 Amphineuren. Biol. Centralbl., Bd. 15, p. 859—869. 



2) L. Plate, Die Anatomie und Phylogenie der Chitonen. Zool. 

 Jahrb., Suppl.-Heft 4, p. 1—243. 



