THE VIEWS OF MIKLUCHO-MACLAY. 405 



on Ceratodus 1 . He says, pp. 30 and 31, " The development of 

 the cerebral hemispheres in Plagiostome Fishes differs from the 

 process by which they arise in the higher Vertebrata. In a very 

 early stage, when the first and second visceral clefts of the 

 embryo Scyllium are provided with only a few short branchial 

 filaments, the anterior cerebral vesicle is already distinctly divided 

 into the thalamencephalon (from which the large infundibulum 

 proceeds below, and the small tubular peduncle of the pineal 

 gland above, while the optic nerve leaves its sides) and a large 

 single oval vesicle of the hemispheres. On the ventral face of 

 the integument covering these are two oval depressions, the 

 rudimentary olfactory sacs. 



" As development proceeds the vesicle of the hemispheres 

 becomes divided by the ingrowth of a median longitudinal septum, 

 and the olfactory lobes grow out from the posterior lateral regions 

 of each ventricle thus formed, and eventually rise on to the 

 dorsal faces of the hemispheres, instead of, as in most Vertebrata, 

 remaining on their ventral sides. I may remark, that I cannot 

 accept the views of Miklucho-Maclay, whose proposal to alter 

 the nomenclature of the parts of the Elasmobranch's brain, appears 

 to me to be based upon a misinterpretation of the facts of develop- 

 ment." 



The last sentence of the paragraph brings me to the one 

 part on which it is necessary to say a few words, viz. the views of 

 Miklucho-Maclay. His views have not received any general 

 acceptance, but the facts narrated in the preceding pages shew, 

 beyond a doubt, that he has 'misinterpreted' the facts of develop- 

 ment, and that the ordinary view of the homology of the parts is 

 the correct one. A comparison of the figures I have given of 

 the embryo brain with similar figures of the brain of higher 

 Vertebrates shews this point conclusively. Miklucho-Maclay 

 has been misled by the large size of the cerebellum, but, as we 

 have seen, this body does not begin to be conspicuous till late in 

 embryonic life. Amongst the features of the embryonic brain of 

 Elasmobranchs, the long persisting unpaired condition of the 

 cerebral hemisphere, upon which so much stress has already been 

 laid by Professor Huxley, appears to me to be one of great 



1 Proceedings of the Zoological Society. 1876, Pt. T. pp. 30 and 31. 



