540 



8. By comparison with the facts observed in other Vertebrata it 

 is established that as many as three elements may contribute to the 

 formation of the choroid plexus of the lateral ventricle in different 

 Vertebrata: a) the roof of the forebrain, b) a band formed by the 

 attenuation of the pallio-thalamic junction, and c) the secondarily 

 thinned caudal part of the paraterminal body. 



9. The high state of development of the cerebral hemisphere in 

 the Dipnoi gives us two alternatives from which to choose as to the 

 relative positions of the Amphibia and Dipnoi: — either the Amphibian 

 hemisphere has passed through a stage corresponding to that of the 

 Dipnoi and has then undergone a secondary retrograde change ; or the 

 Dipnoi are nearer to the main stream, which has led to the origin of 

 the Amniota. 



10. From the earliest stage of development in Lepidosiren, when 

 the rudimentary brain is in contact with the ectoderm, there is an 

 unbroken protoplasmic connection between that area of skin, which 

 developes into the roof of the nasal sac, i. e. the olfactory organ, 

 and that part of the hemisphere-vesicle which later forms part of the 

 olfactory bulb. 



The facts which have been briefly discussed in this communication 

 are of such far-reaching importance that I hope to be able to return 

 to a fuller consideration of them in the near future. 



Writing these notes in Egypt, with no possibiHty of access to the 

 specimens of which I am treating, and without a considerable proportion 

 of the literature essential for such a purpose, I have refrained from 

 entering into the discussion of many points, which have cropped up 

 in the course of the preparation of these notes for publication. 



For the opportunity of examining material of such exceptional 

 interest and for his generosity in attbrding me all the facilities which 

 his laboratory offers it is a pleasure to express my deepest thanks to 

 Professor Graham Kerr. 



Cairo, October 1st, 1908. 



