182 THE VIEWS OF MIKLUCHO-MACLAY. 



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 misin- 

 terpretation of the facts of development." 



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 

 development, 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 importance, and may not im- 

 probably be regarded as a real ancestral feature. Some obser- 

 vations have recently been published by Professor B. G. Wilder* 



1 Anterior brain-mass with Sharks and Skates, American Journal of Science 

 and Arts, Vol. xii. 1870. 



