1878.] Rudimentary Head-Kidney in the Embryo Chick. 443 



value — that is to say, the magnetization of the nickel and cobalt was 

 diminished by pull. But this effect came to a maximum, and began to 

 diminish markedly as if towards zero, when the magnetizing force 

 was diminished. Hitherto the critical value, if there is one, has no£ 

 been reached; but the experiments are being continued to find it, 

 if it is to be found, with attainable degrees of magnetizing force. 



(Addition, May 23, 1878.) 



It had been reached, for nickel, in Glasgow, about the day on which 

 this abstract was written ; advantage having been taken of a kind 

 loan, by Professor Tait, of a much smaller bar of nickel than those 

 which had been specially made for the investigation, and which alone 

 had been previously available. Mr. Thomas Gray, by whom the ex- 

 periments were made, in the Physical Laboratory of the University of 

 Glasgow, in the author's absence, found the critical value of the mag- 

 netizing force for Professor Tait's thin nickel bar to be about 600 times 

 the Glasgow vertical force. 



[The author is indebted to the celebrated metallurgical chemist, Mr. Joseph 

 Wharton, of Philadelphia, for a splendid and unique set of bars, globes, and disks, of 

 pure nickel and cobalt, which he kindly made, at his request, for this and other 

 proposed investigations of electro-dynamic qualities of those metals.] 



X. " On the Existence of a Rudimentary Head-Kidney in the 

 Embryo Chick." By F. M. Balfour, M.A., Fellow of Trinity 

 College, Cambridge, and Adam SedgwiCk, B.A., Scholar of 

 Trinity College, Cambridge. Communicated by Dr. M. 

 Foster, F.R.S., Praelector of Physiology in Trinity College, 

 Cambridge. Received May 20, 1878. 



We have been for some time engaged in an investigation on the 

 mode of growth of the developing Miillerian duct in the chick, and its 

 possible derivation from the Wolffian duct; and, while carrying on 

 our investigations on this point, were struck by some remarkable 

 features of the abdominal opening of the Miillerian duct in its very 

 early condition. We did not for some time pay much attention to 

 these features, but finally devoted ourselves to their interpretation, 

 and have been led to the conclusion that they form the rudiment 

 of a head-kidney, " Vorniere " or " Kopfniere," identical with that 

 present in Amphibia, Marsipobranchii, and Teleostei. We purpose 

 first to give a short account of our observations, and then to proceed 

 to state the grounds on which we have been led to compare the 

 structures we have found with the head-kidney of the Ichthyopsida 



2 G 2 



