70 F. M. BALFOUR. 



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. 



After arriving at the above results with reference to the 

 Sturgeon I proceeded to the examination of the structure of the 

 so-called head-kidney in Teleostei. 



I have as yet only examined four forms, viz. the Pike [Esox 

 lucius), the Smelt [Osmerus eperlanus), the Eel {Anguilla 

 anguilla), and the Angler {Lophius piscatorius) . 



The external features of the apparent kidney of the Pike 

 have been accurately described by Hyrtl.^ He says : ^' The 

 kidneys extend from the second trunk vertebra to the end of 

 the abdominal cavity. Their anterior extremities, which have 

 the form of transversely placed coffee beans, are united together, 

 and lie on the anterior end of the swimming bladder. The con- 

 tinuation of the kidney backwards forms two small bands, sepa- 

 rated from each other by the whole breadth of the vertebral 

 column. They gradually, however, increase in breadth, so that 

 about the middle of the vertebral column they unite together 

 and form a single symmetrical, keel-shaped body,^' &c. 



The Pike I examined was a large specimen of about 58 

 centimetres in length, and with an apparent kidney of about 25 1 

 centimetres. The relations of lymphatic tissue and kidney 

 tissue were much as in the Sturgeon. The whole of the ante- 

 rior swelling, forming the so-called head-kidney, together with a 

 considerable portion of the part immediately behind, forming 

 not far short of half the whole length of the apparent kidney, 

 was entirely formed of lymphatic tissue. The posterior part of 

 the kidney was composed of true kidney substance, but even at 

 16 centimetres from the front end of the kidney the lymphatic 

 tissue formed a large portion of the whole. 



A rudiment of the duct of the kidney extended forwards for a 

 short way into the lymphatic substance beyond the front part of 

 the functional kidney. 



In the Smelt [Osmerus eperlanus) the kidney had the typical 

 Teleostean form, consisting of two linear bands stretching for 

 the whole length of the body-cavity, and expanding into a great 

 swelling in front on the level of the ductus Cuvieri, forming the 

 so-called head-kidney. The histological examination of these 

 bodies showed generally the same features as in the case of the 

 Sturgeon and Pike. The posterior part was formed of the 

 usual uriniferous tubuli and Malpighian bodies. The anterior 



• " Das Uropoetische System d. Knoclienfische," Sitz. d. ' Wieu. Akad./ 

 1850. 



