76 ME. SWALE VINCENT ON THE 



2. The Nature of the Tntertuhidar Material in the Kidneys. 



The lymphatic head-kidney is not in any true sense a very specialized portion of the 

 kidney. By " lymphoid " tissue we mean a variety of retiform connective tissue, in 

 which the meshes of the network are filled up to a large extent with lymph-corpuscles. 

 These differ from the white corpuscles of the blood in that their nuclei show a net- 

 work. Some are as large as white blood-corpuscles, others (the majority) have a 

 minimum of protoplasm, and appear as almost free nuclei. This structure is found 

 typically in a mammalian lymphatic gland. 



Now, on examining the kidney of any fish, the tubules appear to be separated by a 

 variable, often a large, amount of intertubular material, which presents all the features 

 given above characteristic of lymphatic or adenoid tissue. This appearance presents a 

 marked contrast to the compact mass of tubules and Malpighian bodies one sees in a 

 mammalian kidney. The kidney of the frog appears to be intermediate between the 

 mammalian and fish's kidney, in respect of the amount of this intertubular adenoid tissue. 



This tissue varies in amount in different regions of the kidney, but on the whole 

 forms a fairly even bed for the tubules. In Teleosts, as one approaches nearer and 

 nearer to the anterior end of the organ, the amount of adenoid tissue becomes greater 

 and greater until in most cases the extreme anterior extremity of the apparent kidney 

 consists entirely of adenoid tissue. 



3. Histology of the Head-Kidney. 



Structure of the Head-Kidnet op the Ling [Molva vulgaris). — The tissue was 

 hardened in spirit, stained in bulk with hsematoxylin and eosin, and imbedded in 

 paraffin ; sections were then cut with the rocking microtome. 



On examination with a low power, the organ is seen to be obviously a lymphoid 

 structure. Not a trace of kidney-tubules or Malpighian bodies is to be found in any 

 part of the section. The organ is enclosed in a very definite fibrous capsule. There 

 are large blood-vessels ^ in abundance full of red blood-corpuscles. 



With a high power the substance of the head-kidney is seen to be made up of a 

 delicate reticulum enclosing in its meshes closely-packed leucocytes with many red 

 cells apparently free in the reticular spaces, as well as in the large capillaries. In 

 addition, there are many hexagonal crystals of a red colour, most probably oxy- 

 haemoglobin -, and masses of dark pigment-crystals of acicular form, evidently some 

 derivative of haemoglobin. 



I have found practically the same structure in the head-kidneys of the Pleuronectidse, 

 Gadidse, and in fact in all Teleosts I have examined. I have only found this lymphatic 



' And, in some cases, blood-sinuses {vide infra). 



^ The crystals of oxy-haemoglobin obtained from the blood of the Squirrel and Hamster (Halliburton) are 

 described as of this shape, also those from the Mouse (Bojauowski) and Horse (HUfuer and Biicheler). It is 

 tolerably certain that these crystals are of the same character. 



