ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 545 



study of developmental stages shows that it is derived from the epiblastic 

 invagination of the spiracular cleft. It has apparently no relation to the 

 lateral line system of sense organs, and its function is doubtful. From 

 the fact that it is deeply imbedded below the surface, and is intimately 

 connected with one of the efferent branchial arteries, it is suggested that 

 it may function as an organ for testing the osmotic pressure of the blood 

 in these mud-burrowing fishes. The organ apparently does not occur in 

 Ceratodus. 



Cranial Nerves in Chimaera.* — F. J. Cole and W. J. Dakin 

 describe various nerves and their distribution in Chimcera. They note 

 that the discrete nature of the fifth, seventh, and lateral line nerves 

 makes Chimcera a unique fish as regards its cranial nerves. It is 

 presumed that such a simple condition is more primitive than the 

 complex fusions and interminglings that obtain in other fishes. This 

 separation may, however, be purely secondary, just as the form of the 

 brain in Chimcera undoubtedly is ; but, on the other hand, the vagus is 

 also in a very simple and unfused condition. This, indeed, is the 

 condition of the cranial nerves generally. 



Membranous Labyrinth in Elasmobranchs.t — C. Stewart describes 

 the membranous labyrinth and its innervation in Echinorhinus, Cessa- 

 tion, and Rhina. The most noteworthy feature occurs in Rhina squatina, 

 where the otoliths are absent, their place being taken by sand-grains 

 introduced from without through the comparatively large external 

 opening of the ductus endolymphaticus. The sand-grains are often 

 partly cemented into a thin plate. It is not likely that the otoliths are 

 got rid of through the external opening, for they were proved absent in 

 the young unborn examples, although occurring in specimens of the 

 same age of Acanthias vulgaris. 



Vertebrate Fossils of Victoria.} — A. Smith Woodward describes 

 from the Lower Jurassic of Victoria an interesting tooth, which appears 

 to represent a new species of Ceratodus. It differs from all the known 

 Mesozoic teeth of this genus in its narrowness, combined with the 

 straightness of its inner margin and the direction of its second and 

 third denticles. The fossil proves for the first time that the remarkable 

 Dipnoan genus to which it belongs had already reached the Australian 

 region so long ago as the early part of the Jurassic period. At that 

 epoch Ceratodus was still living both in Europe and in North America, 

 while it survived in the African and South American regions at least 

 until the Cretaceous period. From the same rock as that in which the 

 tooth occurred a claw of a carnivorous Dinosaur was taken. It appears 

 to represent a genus related to Megalosaurus, and a detailed description 

 is given. 



Influence of Vertical Currents on Marine Plankton.! — 

 A. Nathansohn finds that Brandt's theory of the influence of denitrify- 

 ing bacteria on the quantitative distribution of the marine plankton is 



* Anat. Anzeig., xxviii. (1906) pp. 595-9 (1 fig.). 

 t Journ. Linn. Soc, xxix. (1906) pp. 439-42 (1 pi.). 

 % Ann. Mag. Nat. Hist., xviii. (1906) pp. 1-3 (1 pi.). 



§ Bull. Mus. Oceanogr. Monaco, No. 62 (1906) pp. 1-12. See also Zool. Zen- 

 tralbl.,xiii. (1906) pp. 225-6. 



