44 DEAN. [Vol. XI. 



the present writer and his observations generally confirmed. 

 His studies of stages earlier than Kupffer had secured do not, 

 however, permit him to believe with the German author, "dass 

 sich beim Stor das urspriingliche Vorderende des Neuralrohres 

 mit Sicherheit hat feststellen lassen," although not doubting 

 that in the Lobus olfactorins impar exists the last connection 

 between brain and epiblast. The earliest Vorderende of the 

 neural canal which the writer has observed occurred in a stage 

 about twelve hours earlier in development than that figured by 

 Kupffer. It has already been noted in PI. IV, Fig. 71. Be- 

 tween this stage and that of Kupffer it has been found that 

 connection exists with the epiblast in front of this point, which 

 corresponds in position with that of Ep"^ of Kupffer's Fig. 13. 

 Sometimes in fact the entire roof of the brain in this region can 

 hardly be regarded as separate from the epiblast : and even a 

 short time before the Lobus comes to be distinctly marked, 

 the anterior region of the brain is for a broad extent {x-x) 

 firmly fused with the epiblast (PI. IV, Fig. 74): that this 

 fusion together with that of the later occurring Lobus is of 

 secondary origin, the present writer is satisfactorily convinced. 

 A discussion of the mode of origin of the hypophysis is 

 reserved for future publication. It may in summary be said 

 that the mode of development of Acipenser appears pecu- 

 liarly specialized, and that many of its essential features in 

 earlier stages seem entirely due to its flattened conditions of 

 growth. 



The latest stage in the development of the central nervous 

 system to be noted in the present paper is that figured in PI. 

 IV, Fig. 52, several hours earlier in development than that of 

 Kupffer's earliest stage (Fig. i). The rather prominent out- 

 line of brain and optic vesicles may in sections be shown to be 

 partly due to pigment contained in the cells of the floors of 

 these cavities. The fore-brain is seen continued far forward, 

 the mid-brain is proportionately large, and the hind-brain is as 

 yet unwidened. The tapering tip of the fore-brain indicates 

 indistinctly the Lobus olfactorins ivtpai% which is here the last 

 point of connection between brain and epiblast. The light- 

 colored margins of the central canal are now clearly marked ; a 



