850 HEAD-KIDNEY IN ADULT TELEOSTEANS AND GANOIDS. 



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 (Osmerns 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 shewed 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 

 swollen part of these bodies, and the part immediately follow- 

 ing, were almost wholly formed of a highly vascular lymphatic 

 tissue ; but in a varying amount in different examples portions 

 of uriniferous tubules were present, mainly, however, in the 

 region behind the anterior swelling. In some cases I could find 

 no tubules in the lymphatic tissue, and in all cases the number 

 of them beyond the region of the well-developed part of the 

 kidney was so slight, that there can be little doubt that they are 

 functionless remnants of the anterior part of the larval kidney. 

 Their continuation into the anterior swelling, when present, con- 

 sisted of a single tube only. 



In the Eel (Anguilla anguilla), which, however, I have not 

 examined with the same care as the Smelt, the true excretory 

 part of the kidney appears to be confined to the posterior por- 

 tion, and to the portion immediately in front of the anus, the 

 whole of the anterior part of each apparent kidney, which is 

 not swollen in front, being composed of lymphatic tissue. 



LopJiius piscatorius is one of the forms which, according to 

 Hyrtl 1 , is provided with a head-kidney only, i.e. with that part 

 of the kidney which corresponds with the anterior swelling of 

 the kidney of other types. For this reason I was particularly 

 anxious to investigate the structure of its kidneys. 



1 "Das Uropoetische System der Knochenfische," Silz. d. U'icn. Akad., 1850. 



