No. 470] 



UNITY OF GNATHOSTOME TYPE 



85 



parts, which has until recently been an obstacle to most zoologists 

 in establishing the homologies between the amphioxus brain and 

 the brain of the Craniata, and even to-day very few anatomists 

 know enough about the structure of amphioxus to be able to 

 establish the homologies which are existent. 



Apparently the first zoologists to note the presence of the am- 

 phioxus brain were Leuckart and Pagenstecker, who homol- 

 ogized the entire brain vesicle of amphioxus with four ventricles 

 of the Craniata. 



Owsjannikow later held the same view. In 1858, Professor 

 Huxley, after careful examination, decided that the amphioxus 

 neurocoele was the equivalent of the thalamencephalon of the 



In 1860, Wilhelm Miiller concluded that it corresponded with 

 the thalamencephalon and the prosencephalon of the Craniata. 

 He further determined the location of the pigment in the anterior 

 end of the brain tube and found that the pigment granules were 

 located in the anterior ends of the brain cells. He also discovered 

 that the olfactory pit was connected with the anterior end of the 



In 1861, Langerhans discovered the true relation of the olfac- 

 tory epithelium of the olfactory tubercle of the brain. He decided 

 that the amphioxus brain included the whole of the primitive 

 Craniate brain. 



In 1891, I described in a brief way some of the anatomical fea- 

 tures of the amphioxus, giving the following account of the brain. 

 "The anterior end of the neural axis of amphioxus is a brain and 

 corresponds with a certain definite portion of the brains of other 

 vertebrates. Its anterior wall is the homologue of the lamina 

 terminalis of other vertebrate brains, and the anterior j)ortion of 

 its unpaired ventricle is the thalamocd^le." 



"T would define the vertel)rate brain as follows: the 'vertebrate 

 brahi' is that portion of the anterior part of the axial '^^^^''^^^^^ 



of\hr(v,'mllVanaL'lhi.-l. eaiTi*--! ont into all Mrn.ture. lornu-d 

 All further additions to this simple brain (ami)hi()xu.s) are made 



