ON THE HEAD KIDNEY OF BDELLOSTOMA. 175 



tain in preserved specimens a blood-clot^ and, therefore, in the 

 living animal blood. 



The above description applies to the main body of the duct ; 

 anteriorly it gives off a bunch of tubules, similar in all respects 

 to those given off from its sides (see diagram, fig. 2), while pos- 

 teriorly it ends in a mass of tissue (figs. 2 and 6 and 7), resem- 

 bling the trabecular supporting tissue of a lymphatic gland. 

 Fig 6 shows a portion of the periphery of a section through 

 this tissue. It is seen to consist of a network of nucleated, 

 branched connective-tissue cells, with elongated meshes, in 

 which are several scattered blood-corpuscles (b. c). 



This lymphatic tissue is covered by a well-marked epithelium 

 (b), forming the capsule of a large glomerulus (figs. 2 and 6, 

 (/I.), which lies close to it. From this glomerulus strands of 

 blood-vessels pass off at frequent intervals into the lymphatic 

 tissue. Such a strand is figured at x in fig. 6. 



Owing to the impossibility of injecting a capillary plexus in 

 an animal which has been preserved in chromic acid, I have not 

 been able to obtain any very definite proof that blood can pass by 

 these strands of vessels into the lymphatic tissue of the duct, 

 and so into its lumen ; but I am strongly inclined to believe 

 that this is the case. 



I have occasionally seen capillaries leading directly from the 

 lumen of the central duct, though I have been unable to follow 

 them for any distance. 



Until, however, further observations on fresh specimens can 

 be made, I venture to think that I have shown tolerably good 

 reason for assuming that the blood enters the lumen of the 

 central duct of the ^'head kidney" through the glomerulus at 

 its posterior extremity. 



In some of my series of sections there is a considerable in- 

 terval between the glomerulus just described and the segmental 

 duct, which is occupied by nothing but connective tissue. In 

 other, presumably younger specimens, I find traces of a 

 continuation of the renal duct into the head kidney ; though 

 in no case have I seen a continuous lumen in the connecting 

 piece. 



