90 



ANATOMY OF AMPHJOXUS. 



Anteriorly in the region of the cranial nerves the lumen 

 of the central canal widens out into a relatively spacious 

 vesicle, known as the cerebral vesicle (Fig. 45). In young 

 individuals this cavity opens by an aperture called the 

 neiiropore into the base of an epidermal pit, which we 

 have already described under the name of the olfactory 

 pit. Later on the neuropore closes up, but its former 



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Fig. 45. — A. Brain and cranial nerves of a young Amphioxus of 3 mm. length. 

 B, C, D. Sections through different portions of biain : B, through neuropore and 

 cerebral vesicle; C, through the intermediate portion, and /), through the dorsal 

 dilatation of central canal. ("After Hatschek.) 



ill. Notochord. c.v. Cerebral vesicle, dil. Dorsal dilatation (Hatschek't fossa 

 I hoiiil'oidaiis). e. Eye-spot. np. Neuropore. olf. Olfactory pit. 



/, //. First and second cranial nerves. 



presence is indicated by a shallow groo\'e at the base of 

 the otherwise solid stalk connecting the olfactory pit with 

 the roof of the brain. 



Behind the cerebral vesicle the Inmen of the central 

 canal widens out in its dorsal portion independently of 



