210 



MARINE BIOLOGICAL LABORATORY. 



sense-organs of the auditory complex and of their canals. 

 It is the morphological value of that sense-organ which, 

 ever since its discovery by Retzius, has been such a 

 source of discussion and investigation ; viz. the macula 

 acustica neglecta, supposed by some to belong to the 

 utriculus J by others, to the sacculus in the older sense. 



A 



B 



i^J Clo 



OQ 



CD €> i> 



O 



Fig. 14. 



A Auditory vesicle. 



B Utriculo-sacculus. 



C Utriculo-sacculus -I- two ampullary canals. 



D Utriculo-sacculus -t- two ampullary canals and lagenar canal. 



Stage A represents the undivided superficial sense-organ of the verte- 

 brate ancestor, as it is invaginated from the surface and enclosed within the 



