L68 SUMMARY OF CURRENT RKSEARCHES RELATING TO 



ectoderm, fuse with it, and thus the gill-slits originate. Obviously they 

 are endodermal, and in the further development of the gill apparatus 

 there is no change in this. In Teleosteans and Ganoids a reverse process 

 takes place ; there are ectodermal ingrowths, with very slight outgrowths 

 from the gut. Ultimately ectoderm reaches the gut wall in all the slits, 

 and thus the presence of skin teeth on the inner edges of the arches and 

 in the gnllet is accounted for. In Selachians an intermediate condition 

 exists, there being gut folds which blend with slight invaginations of 

 ectoderm. The largest part is thus endodermal at first, but later the 

 conditions are reversed. The endodermal part of the pockets disap- 

 pears completely, and in mature animals the inner openings alone of the 

 slits are lined by it, and thus a similar condition to that in Teleosteans 

 is reached. The development of the gill apparatus is also considered in 

 the paper. 



Development of Kidney in Elasmobranchs.* — I.Borcea has studied 

 this in Mustelns and Acanthias, and finds that the Elasmobranch kidney 

 is embryologically of the same value as that of higher vertebrates. 



Development of Myocardium in Teleosts.f — J. Boeke finds that in 

 Mimenoid larva? the myocardium forms a syncytium, as others have 

 observed in mammals. During the differentiation of the fibrils, the cell 

 limits, at first distinct, are lost, and the cells fuse into a syncytium. The 

 author indicates the importance of this fact in relation to the physiology 

 of the heart muscle-fibres. 



b. Histology. 



Intra- and Extra-Cellular Nerve Nets in Vertebrates.! — L. Auer- 

 bach gives proof for his view, brought forward in the paper, that the end 

 branches of the axis cylinder do not remain separate from each other, 

 but, contrary to the usual idea, blend in a peculiarly continuous net- 

 work. 



Peripheral Nerves of Vertebrates.! — R. G. Harrison finds that the 

 axis cylinders of motor nerves are developed in a normal manner in frog 

 embryos, in which the occurrence of Schwann cells has been prevented 

 by the early cutting out of the " Ganglienleiste." The nerves are here 

 naked fibres, which can be followed as such .into the ventral part of the 

 tail musculature. The sensory nerves of the tail consist in Triton 

 larvae, first of naked branched fibres, which from their origin in the 

 hinder cells and the spinal ganglia to their termination show no- 

 Schwann cells. These cells only appear after the fibre is formed ; they 

 come forward gradually from the centre to the periphery, as may be seen 

 by a comparison of different stages, and by direct observation on the 

 fins of living tadpoles. The Rohon-Beard hinder cells of the frog 

 embryo early throw out protoplasmic continuations, which stretch under 

 the skin and become nerve fibres. The end of the developing nerve- 

 fibre consists of a thickening with delicately branched pseudopodic ter- 



* Comptes Rendue, exxxix. (1904) pp. 747-9. 



t K. Akad. Wetenschappen Amsterdam (Proc. Sect. Sci.) yi. (190">) pp. 218-25 

 (1 pi.). % Anat. Anzeig., xxv. (1904) pp. 47-5:"). 



§ S.B. Niederrhein Gee. Nat. Bonn. (1904) pp. 1-7. 



