THE LYMPHATICS. 



313 



with the blood-capillaries, in the occurrence of nuclei on the 

 inner side of the very delicate, structureless membrane, whilst 



they differ from them in being furnished with short, jagged 

 processes with prolongations. The diameter of the lymphatic 

 capillaries in this situation is 0002 — 0*01 5'", and the two main 

 trunks of the tail, like those of the blood-vascular system 

 itself, have a perfect capillary structure. 



In what way these capillary lymphatics are changed into 

 the larger lymphatic canals has not been seen by any one, or at 

 all events has not been investigated. The finest vessels, which 

 have elsewhere come under my observation, had a diameter of 

 i — \ — i'", and these, except in the thickness of the individual 

 layers, corresponded in all respects with the larger vessels of 

 1 — 1J'". The latter, the medium-sized lymphatics, present three 



Fig. 288. Capillary lymphatic from the tail of the Tadpole, x 350 diam.: a, mem- 

 brane ; b, processes formed by it ; c, remains of the contents of the cells forming 

 these vessels, in which nuclei are concealed ; e, caecal terminations of the vessels ; f 

 one of these terminations, still pretty distinctly recognisable as a formative cell ; g, 

 isolated formative cells about to join with the actual vessels. 



