472 BERTRAM H. WATERS. 
the primitive neuron, i. e. the first ten or eleven segments, by 
a direct differentiation and specialisation, the complex region 
known as the encephalon has been evolved. That striking 
fact of Vertebrate embryology, viz. the rapid increase of the 
anterior brain region and its great differentiation, seems to 
account for the relatively greater size of the fore- and mid- 
brain segments, and their early degeneration, and for the per- 
sistence of those in the hind-brain, which is more primitive in 
character. 
BIBLIOGRAPHY. 
1. AuLBoRN.—‘ Ueber die Segmentation des Wirbelthier-Korpers,’ Gottin- 
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2. Batrour.—‘ Comparative Embryology,’ 1885. 
* Development of Hlasmobranch Fishes,’ 1878. 
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4, BéranEcK.—(a) “ Recherches sur le développement des nerfs craniaux 
chez les Lézards,” ‘ Recueil Zoologique Suisse,’ t. i, p. 557, 1884. 
(6) ‘ Replis médullaires du Poulet,” ‘ Recueil Zoologique Suisse,’ 
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Anat. und Physiol.,’ 1883. 
“Ueber Analogen yon Sinnensorganen an Facialis u. s. w.,” ‘ Archiv 
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