13 r. M. BALFOUR. 



0)t Ike Nature of the Organ in Adult Teleosteans and 

 Ganoids, loliicli is usuallj/ regarded as the Head-Kidney 

 or Pronephros. By F. M. Baleour, LL.D., F.E.S., 

 Fellow of Trinity College^ Cambridge. 



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 aUied 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 tissue. Thus the whole of that 

 'part of the apparent kidney in front of the ureter, inchuling 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 

 Stannius, at least I so interpret a note of his in the second 

 edition of his ' Comparative Anatomy,' p. 263, where he 

 describes the kidney of the Sturgeon as being composed of two 

 separate parts, viz. a spongy vascular substance (no doubt the 

 so-called head-kidney) and a true secretory substance. 



1 I am about to publish in conjunction with Mr. Parker a full account 

 of the anatomy and development of Lepidosteus, and shall therefore in 

 this paper make no further allusion to it. 



