The Infra-cerebral Organs of Peripatus. 



By 

 William J. Dakin, D.Sc, F.Z.S., P.L.S., 



Derby Professor of Zoology, University of Liverpool. 



With 4 Text-figures. 



Attached to the ventral surface of the supra-oesophageal 

 ganglion of Peripatus and hanging therefrom are two small 

 vesicles. They were discovered as far back as 1853 before 

 Peripatus was regarded as an Arthropod, and Grube, their 

 discoverer, considered them to be auditory organs (8). 



In 1883, Balfour, in his classical description of the anatomy 

 of Peripatus capensis(2), described the structure of these 

 vesicles, and after a statement detailing their shape and 

 position added that each consisted mainly of ganglion cells. 

 He continued with the following words : ' In its interior is 

 a cavity with a distinct bounding membrane. ... At its free 

 end is placed a highly refractive, somewhat oval body, probably 

 forming what Grube describes as a dark spot, half embedded 

 in its substance, and kept in place by the sheath of nervous 

 matter surrounding it. It is difficult to offer any interpretation 

 of the nature of this body. It is removed considerably from 

 the surface of the animal, and is not, therefore, so far as I can 

 see, adapted to serve as an organ of hearing.' 



Three years after the appearance of Balfour's paper. Kennel 

 (11) followed the development of the infra-cerebral vesicles and 

 discovered that they were apparently homologous with certain 

 groups of cells situated between the legs — and known as 

 the ' ventral organs ' (see Text-fig. 1). 



This was confirmed by Sedgwick (15) in 1888, and the 



