v. i3 



LABYRINTH OF LAMPREYS 



109 



In the lamprey the lateral line organs are very simple (Fig. 71), being 

 open to the exterior and not sunk in a canal as in higher forms. The 

 rows are somewhat irregular, especially those on the body. 



13. Vestibular organs of lampreys 



The labyrinth may be considered as a specialized portion of the 

 lateral line system, concerned with recording the position of the head 



end. 



mac.laq. \ mac.ut. 

 3 mac. sac. 



smp.p. 



amp a. 



Fig. 72. Labyrinth of right side, seen in lateral view. A and B, 



Lampetrci, c, Myxitie. 



a.c. anterior canal; amp. a. and p. anterior and posterior ampullae; cil. 



ciliated chamber; cr.a. and p. cristae; end. endolymphatic duct; lag. 



lagena; mac. lag., neg., sacc, ut. maculae of the lagena, neglecta, 



saccule, and utricle; p.c. posterior canal. (After de Burlet.) 



and angular accelerations. There is no evidence to decide whether 

 lampreys can respond to sound. The labyrinth develops by an in- 

 pushing of the wall of the head, and this then becomes closed off from 

 the exterior. Internal foldings divide up the sac into a number of 

 chambers, which differ considerably from those of gnathostomes. 

 There is a large central vestibule, into which open below several 

 partially separate sacs, provided with patches of sensory hairs. These 

 correspond, from in front backwards, to the maculae of the utricle, 

 saccule, and lagena of higher forms (Fig. 72). The hairs of the maculae 

 are loaded with otoliths. There are only two broad semicircular 

 canals, corresponding to the anterior and posterior vertical canals 

 of other vertebrates, each with an ampulla, containing a receptor 

 ridge, the crista. Also opening to the vestibule are two large sacs, 



