480 - ALFRED GIBBS BOURNE, 



macerating corpuscles; there are^ in addition, a large number 

 of very fine filaments, which tend to have a radiating arrange- 

 ment with regard to clumps of corpuscles, or sometimes to bind 

 them together. These may be observed continually moving to 

 and fro, a movement caused, I believe, by the ciliary current, 

 and not in any way intrinsic. The filaments present an even 

 diameter, are exceedingly fine, and sometimes much twisted ; 

 they readily stain with iodine. They are shown as seen with 

 Hartnack^s No. xii k immersion in fig. 55. I think these 

 filaments are most probably somewhat of the nature of fibrin, 

 and are formed from time to time in the blood in abnormal 

 conditions. The possibility of their being leptothrix filaments 

 entered my mind, but they are always present, and no other 

 bacteria forms are ever visible, both of which facts militate 

 strongly against this view. I have noticed somewhat similar 

 filaments in the dilatations following upon the funnels in 

 Nephelis, Clepsine, and Hirudo, although nowhere are 

 they developed to the extent that they are in Pontobdella. 



Network of Tubules. — The tubules consist of simple or 

 branched cells with an intracellular lumen. 



In the fresh state the wall often presents surface markings 

 similar to those I have described in Hirudo (1. c); these are 

 shown in fig. 56. In optical section the walls of the lumen ex- 

 hibit a radiating structure (see figs. 57, 58, &c.). The cells 

 attain a great size, fig. 58 showing a single cell — a cell con- 

 taining csecal diverticula of the lumen. In some places the 

 wall of the lumen is thrown up into little vesicles, generally 

 arranged in groups. At such places the wall becomes much 

 thinned out (fig. 57), and the lumen must come into very close 

 physiological relations with its surroundings. 



The lumen may vary in extent from spot to spot, and 

 from time to time, the walls being capable of distension. Fig. 

 60 shows the appearance of a portion of the network in the 

 fresh condition. Fig. 59 shows a portion in a preparation 

 which has been macerated in 10 per cent, nitric acid. An 

 examination of this figure will show how few nuclei occur, and 

 consequently how large and much branched must individual 



