ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 211 



is a factor influential in shortening the last stages of metamorphosis. 

 With this other parallel phenomena are compared, and the author emphasizes 

 the extent to which the economy of the organism is self-adjusting. 



Absorption of the Tadpole's Tail.* — Dr. D. Barfurth has made a 

 careful study of the exact manner in which the tadpole's tail gradually 

 disappears. (1) The epidermis cells are simply atrophied, grow old, 

 shrivel up, and die. (2) In the capillaries and smaller vessels the lumen 

 disappears with disuse, and the elements on the walls fall off in small 

 fragments to be eaten by leucocytes or dissolved. (3) The notochord and 

 nerve-fibres seem to exhibit similar degeneration. The spinal cord cells 

 become turbid and infiltrated with nuclear debris. (4) The muscle-fibres 

 exhibit disruption into sarcolytes, fatty degeneration, and nuclear prolifera- 

 tion in the perimysium internum. (5) Leucocytes appear throughout de- 

 vouring the debris, and carrying it to the lymph-vessels. (6) The material 

 is used up for the development of more essential organs and tissues. 



These degenerative processes begin only when the tissues are in process 

 of death. The phagocytes appear, as Metschnikoff notes, when definite 

 irritant elements or foreign bodies are present. The tissues begin to die in 

 consequence of insufficient nutrition, and this in consequence of the cessation 

 of trophic influence from the nervous system. The trophic influence ceases 

 because the function of tail, after the appearance of the fore limbs, is 

 superfluous. The weal of the entire organism finds expression through the 

 central nervous system. 



Intra-ovarian "Egg in Osseous Fishes.f — Dr. E. Scharflf has studied the 

 intra-ovarian egg, chiefly in Trigla gurnardns. 



In the youngest ova the nucleus occupies nearly the whole cell ; the 

 nucleoli being peripheral. Later, the surrounding protoplasm increased, and 

 a darker internal portion can be distinguished, which arises from the 

 nucleus. When the egg has almost reached its final size, the nucleus 

 shrinks, and protuberances appear on all sides ; these become constricted 

 off and travel to the periphery of the egg. The author does not consider 

 that the nucleus, although it degenerates, ever entirely disappears. 



The most external membrane is the "zona radiata," within which a 

 semi-fluid layer exists, which later disappears. A peculiar modification is 

 noticed in the follicle cells of the egg of Blennius jphotis. As to the 

 development of the ova, the author is inclined to think that only one cell ig 

 concerned. The egg-membranes do not appear till after the follicle. 



Growth of Embryos of Osseous Fishes.f — M. L. F. Henneguy finds 

 that a series of longitudinal sections of the embryo of osseous fishes shows 

 that, during the extension of the blastoderm on the vitellus, the embryo 

 grows chiefly in the part comprised between Kupffer's vesicle and the 

 protovertebrse ; new somites are constantly formed in the anterior portion 

 of this region. If this view be correct, it can hardly be brought into 

 agreement with the theory of His, though it is compatible with the 

 hypothesis of Kupffer and Oellacher. M. von Kowalewski, who has been 

 studying recently the development of the ova of such Teleosteans as have 

 ellipsoidal eggs, has been able to prove that, at the moment when the 

 germinal layers are differentiated, the blastoderm grows along the whole of 

 its periphery, but that the caudal extremity of the embryo remains fixed 

 on a point of the vitellus. The author thinks it is very probable that the 

 same is true of osseous fishes with spherical eggs. 



* Arch. f. Mikr. Anat., xxix. (1887) pp. 35-60 (2 pis.). 



t Proc. Eoy. Soc, xli. (1886) pp. 447-9. % Comptes Rendus, civ. (1886) pp. 85-7. 



