XXIII. ON THE NATURE OF THE ORGAN IN ADULT TE- 



LEOSTEANS AND GANOIDS, WHICH IS USUALLY RE- 

 GARDED AS THE HEAD-KIDNEY OR PRONEPHROs 1 . 



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 I 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 abdo- 

 minal cavity. In front each of these bands first becomes con- 

 siderably 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 shew that in this part the kidney is really 

 formed of uriniferous tubuli with numerous Malpighian bodies. 

 Just in front, however, of the point where the ureter ends the 

 true kidney substance rapidly thins out, and its place is taken 

 by a peculiar tissue formed of a trabecular work filled with cells, 



1 From the Quarterly Journal of Microscopical Science, Vol. XXII., 1882. 



2 I am about to publish, in conjunction with Mr Parker, a full account of the 

 anatomy and development of Lepidosteus [No. XXII. of this edition], and shall 

 therefore in this paper make no further allusion to it. 



