On the Natuee of the Organ in Adult Teleosteans 

 and Ganoids, tvhich is usually regarded as the 

 Head-Kidney or Peonepheos. Bj F. M. Balfoue, 

 LL.D., F.R.S., Fellow of Trinity College, Cam- 

 bridge. 



While working at the anatomy of Lepidosteus I was led to 

 doubt the accuracy of the accepted accounts of the anterior part 

 of the kidneys in this and in allied species of Fishes. In order 

 to test my doubts 1 first examined the structure of the kidneys in 

 the Sturgeon (Acipenser), of which I fortunately had a well- 

 preserved specimen. 



The bodies usually described as the kidneys consist of two 

 elongated bands, attached to the dorsal wall of the abdomen, and 

 extending for the greater part of the length of the abdominal cavity. 

 In front each of these bands first becomes considerably narrowed, 

 and then expands and terminates in a great dilatation, which is 

 usually called the head-kidney. Along the outer border of the 

 hinder part of each kidney is placed a wide ureter, which ends 

 suddenly in the narrow part of the body, some little way behind 

 the head-kidney. To the naked eye there is no distinction in 

 structure between the part of the so-called kidney in front of 

 the ureter and that in the region of the ureter. Any section 

 through the kidney in the region of the ureter suffices to show 

 that in this part the kidney is really formed of uriniferous 

 tubuli with numerous Malpighian bodies. Just in front, how- 

 ever, of the point where the ureter ends the true kidney sub- 

 stance rapidly thins out, and its place is taken by a peculiar 

 tissue formed of a trabecular work filled with cells, which I 

 shall in future call lymphatic tis>sue. T/ius the whole of that 

 part of the apparent kidney in front of the ureter y including the 

 whole of the so-called head-kidney, is simply a great mass of 

 lymphatic tissue, and does not contain a single uriniferous tubule 

 or Malpighian body. 



The difference in structure between the anterior and posterior 

 parts of the so-called kidney, although not alluded to in most 

 modern works on the kidneys, appears to have been known to 



