TNFRA-CEKEBRAL ORGANS OF PERIPATUS 



413 



The cavity of the vesicle is most usually empty, but some- 

 times contents are present, and the most conspicuous example 

 of this kind has been figured (Text-fig. 2). In this specimen 

 there is a non-granular mass surrounded by a number of 

 concentric lamellae — almost like a decalcified concretion. The 

 occasional presence of an enclosed body is very interesting. 



Text-fig. 4. 



Diagram illustrating development of infra- cerebral vesicles in 

 Peripatus occiden talis. 



At first it was thought to be due to fixation, but there is no 

 reason to believe that such is the case. Evidently the vesicle 

 cells may sometimes secrete into the central cavit3^ Thus 

 a feature recorded by Balfour has again been found and 

 in another species. The few writers who have mentioned 

 the infra-cerebral vesicles since the date of Balfour's paper 

 seem to have doubted its occurrence. No cilia are found within 

 the vesicle nor is there any very definite lining membrane. 

 NO. 263 G g 



