one of these was briefly described by Kner in 1869*; the other was for many years in the Museum of the Otago University, Dunedin, and was forwarded to me for investigation by the present curator, Professor W. B. Benham, D.Sc., to whom I desire to express my indebtedness for his great kindness.
The specimen which I have thus had the opportunity of investigat- ing Avas labelled in the handwriting of the late Professor T. J. Parker, F.R.S. "Ammoccetes stage of Geotria Opoho Creek. Jany., '84. Chromic and Osmic." It; had evidently been preserved with the utmost care, and proved, in spite of its age, to be in an admirable state for histological investigation.
The total length of the specimen was about 57 mm., and the greatest diameter in the middle 3'5 mm. With a view especially to the study of the parietal organs, the head region was cut into a series of transverse sections b}^ the usual paraffin method, and the sections were stained on the slide ; for staining, carbol-fuchsin proved satisfactory.
On examination, the sections thus prepared showed not only a well-developed parietal eye and the structures usually associated there- with, but also a pair of conspicuous ciliated grooves lying in the roof of the brain in the neighbourhood of the posterior commissure. These grooves run longitudinally from the recessus sub-pinealis to the hinder margin of the posterior commissure. They are most conspicuous beneath the commissure itself (figs. 1, 2), in which region they are
FIG. 1.
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.Ch.Pl
Com. P.,
-M.C.
Tr.
Tr
- " Keise der Oslerreichischen Fregatte Novara um die Erde,"' Zoologie,' 13J. 1,
Fiscbe, p. 421 .
