ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 409 
ever, Mr. Tomes gives his authority to the usage which still calls this 
layer enamel. 
Parathyroid Glands.* * * § — Dr. D. A. Welsh has made a critical, ana- 
tomical, and experimental study of the parathyroid glands ; but of this 
only the first part is published. It gives a highly useful historical 
digest of the literature concerning these puzzling bodies. 
Minute Structure of Notochord.j — Prof. F. K. Studnicka remarks 
that the tissue of the notochord is usually described as very simple, — 
a superficial epithelium, and large internal vacuolated elements, the 
exact nature of which has been often disputed. Ebner, however, rather 
changed this view by showing that the notochordal tissue was in no way 
degenerate, hut rather the reverse. 
Studnicka describes the structure in Petromyzon , Myxine , Chimsera , 
Selachians, several Ganoids and Teleosts, Ceratodus , Protopterus , and 
some Amphibians. The cells have no real membrane, nor anything 
comparable to cartilage. The presence of intercellular connections and 
fibrillations in the ectoplasm suggests affinity with epidermis and epithe- 
lium. At the same time, it must be noticed that the germinal zone 
(Keimzone) of the notochordal tissue — in other words, the epithelium — 
has here and there the capability of forming cartilage. In many cases, 
nevertheless, the cartilage described in the notochord is quite extraneous 
in origin. 
c. General. 
Light-Limit in Water 4 — Dr. L. Linsbauer is much more cautious 
than some are in regard to the liglit-limit in water. We neither know 
the composition of the light at different depths, nor the limit beyond 
which light fails to penetrate. It seems certain that a depth of 500 metres 
does not represent the limit at which chemical rays may be operative. 
The greatest depth recorded for a plant, not a Thallophyte, is 60 m., 
at which Forel found a moss ( Thamnium alopecnrus ) in Lake Geneva. 
Alg£8 occur at much greater depths, though they are certainly very 
sparse beyond several hundred metres. More exact experiments are 
necessary before we can speak definitely in regard to a quite light-less 
( aphotische ) region. The author has devised an arrangement for testing 
the colour and intensity of the light at various depths. 
Bristle-like Structures on a Shark. § — Prof. A. Brandt observed 
twenty-seven years ago the presence of numerous bristle-like structures 
on the snout of a shark, probably SelacJie maxima ; and with the assistance 
of his colleague Prof. W. Reinhard he has now investigated them. They 
differ conspicuously from Mammalian bristles in the deposition of cal- 
careous corpuscles in the papilla and in the fibrous tissue. The author 
argues for the consideration of the hypothesis that hairs and teeth may 
be homologous structures. 
Functions of Hypophysis Cerebri. || — E. de Cyon has been led on 
experimental evidence to regard the hypophysis, like the thyroid, as an 
* Proc. Scot. Micr. Soc., ii. (1896-7) pp. 128-43. 
f SB. Bohm. Ges. Wiss., 1897 (ii.) No. xlv. 71 pp. (2 pis.), 
j Verh. K. K. Zool.-Bot. Ges. Wien, xlviii. (1898) pp. 167-70. 
§ Biol. Centralbl., xviii. (1898) pp. 257-70 (10 figs.). 
|| Comptes Rendus, cxxvi. (1898) pp. 1157-60. 
