494 On a Pair of Ciliated Grooves in the Brain of the Ammoccete. 



Probably, however, the closest physiological parallel is really to be 

 found in the ciliated groove which, according to Beard, is to be found 

 lying " at the base " of the neural tube in the embryos of nearly all 

 vertebrates,* and which also doubtless serves to promote the circula- 

 tion of the fluid in the cavity of the central nervous system. 



DESCRIPTION OF FIGURES. 



All the figures, except fig. 2, were drawn with the aid of the camera lucida under 

 Zeiss objective A, with eyepiece No. 3. Fig. 2 was drawn with the aid of the 

 camera under Zeiss objective D, eyepiece No. 3. 



Fig. 1. Transverse section of the brain of the New Zealand Ammoccete through 

 the region of the posterior commissure. 



Fig. 2. Portion of similar section of the same specimen a short distance in front 

 of the last, showing the histological structure of the ciliated grooves. 



Fig. 3. Transverse section of the sam specimen just behind the posterior com- 

 missure, showing the ingrowth of the choroid plexus of the mid- 

 brain to form a A'ertical septum. 



Fig. 4. Transverse section of the brain of the Owens College Ammocccte through 

 the region of the posterior commissure. 



Fig. 5. Similar section through the region of the recessus sub-pinealis. 



Fig. 6. Similar section at about the level of the hinder margin of the posterior 

 commissure. 



Explanation of Lettering. Ar. T., arachnoidal tissue. C.G., ciliated groove. 

 Ch. PL, choroid plexus. Co m. P., posterior commissure. G.H.R., right ganglion 

 habenulaj. //., lufundibulum. Her, aquceductus Sylvii or iter. M.b.l., left 

 Meynert's bundle. M.b.r., right Meynert's biiudle. M.C., connective tissue 

 brain case (membranous cranii). U.S., recessus sub-pinealis or iiifra-pinealis. 2V., 

 trabecultB'cranii. 7'. 3, third ventricle. 



* ' Anatomischer Anzeiger,' vol. 3, pp. 902, 903. 



