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.
