ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 17 



Tlio tubules of the metancpliros arise independently in the blastema 

 surrounding the ureter, and probably also as branches from it. It 

 would seem therefore that pronephros, mesonephros, and metanephros 

 are heterodynamous organs only connected by their relations to the 

 Wolffian duct. The glomus of the pronephros is distinct in origin, 

 character, position, and extent, from the glomerulus of the metanephros. 



Blastopore of Frog 1 .* — Prof. H. V. Wilson has studied the history 

 of the blastopore of the frog, especially Corophilus feriarum Baird. 

 Yolk-cells adjacent to the dorsal lip of the blastopore gradually dis- 

 apjicar under that lip, and this is interpreted as due to outgrowth on 

 the part of the dorsal lip. The same happens ventrally, and is similarly 

 interpreted. Ectoderm cells close to the dorsal lip and close to the 

 ventral lip gradually disappear round their respective lips, and must, 

 it would seem, become part of the archenteric lining. 



After comparing his experiments, it seems to the author that his 

 results are all explicable on the theory advanced by Assheton (1894), 

 Whitman, and Eycleshymer (1895), that dorsal and ventral lips overgrow 

 the yolk, from the places of their first appearance to the lower pole — 

 the neural plate hence being formed in part on the black hemisphere, 

 and in part by the backward growth of the dorsal lip over the white 

 hemisphere, as Pfliiger (1883) thought was possibly the case. 



Thymus-Element in Spiracle of Raia.f — Dr. J. Beard has been 

 able to prove that the structure named by Van Bemmelen the " ventral 

 vesicular follicle of the spiracle," is really a rudimentary thymus-ele- 

 ment. He finds that it arises as a placode of the gill-pouch, and with 

 the rupture of the latter comes to be epiblastic in position. It later 

 acquires a covering of ordinary epiblast, is penetrated by blood-capil- 

 laries, and divided by connective-tissue septa, and its epithelium gives 

 origin to leucocytes. At a later stage it becomes more or less con- 

 stricted off from the branchial epithelium, but apparently the separation 

 is not complete, as in the case of an ordinary thymus-elernent. 



Regeneration of Lens.f — Herr A. Fischel vindicates against G. 

 Wolff's criticism his previously st;tted result that the iris — especially 

 the lower half — is able to form lens-fibres, and a small but indisjmtable 

 lens. Cases where lens-lesions had occurred were rejected. 



b. Histology. 



Comparative Histology of Vertebrata.§ — Dr. A. Oppel has pub- 

 lished the third instalment of this immense work. Two previous parts 

 dealt with the gullet, stomach, and intestines; this deals with the mouth, 

 the tongue, the salivary glands, the liver, and the pancreas. The method 

 of treatment is in great part historical, and there is much physiological 

 as well as histological information. Various authorities have already 

 spoken highly of this work of reference. 



Structure of Human Epidermis. || — Dr. Ludwig Merk finds that the 

 horny cells of the human skin contain three distinct substances: — (1) a 



* Anat. Anzeig., xviii. (1900) pp. 209-39 (16 figs.). 



t Tom. cit., pp. 359-63. J Tom. cit., pp. 324-6. Cf. this Journal, 1898,^p. 406. 

 § 'Lehtbuch der vergleichenden mikioskopischen Anatomie der Wirbeltiere,' 

 iii. Teil, Jena. 1900, Svo, x. and 1180 pp., 679 figs., and 10 pis. 

 || Arch. Mikr. Anat., lvi. (1900) pp. 525-35 (2 pis.). 



Feb. 20th. 1901 C 



