1?Y S. ,T. JOHNSTON. 295 



brilliant red, while the muscle and connective tissues, cuticle and 

 spines are stained light to dark brown Ijy the oi-ange G. The 

 chief drawback is that these stains are not nearly so permanent 

 as the hseinatoxylin. 



For the excretory system, besides the living worms, in which it 

 is best studied, unstained specimens, cleared in xylol-phenol and 

 mounted in Canada balsam, w^ere most satisfactory 



Tn addition to working on fixed and stained material, I have 

 also, as Looss(-l:8,53), Luhe(10,60) and others recommend, studied 

 the worms alive, mounted in salt solution. Most of these worms 

 will keep alive for 48 hours or longer in salt solution, and will 

 even live mounted im a slide and slightly compressed by the cover- 

 glass, for a number of hours. The slight pressure makes the 

 worms sutticientl}^ transparent for one to be able to make out 

 practically all the details of their internal structure. It was 

 while working in this way, that I was able to follow out the pro- 

 cess of egg-formation in Dolichosaccus, as well as to see the 

 Laurers canal in action, and to observe the early stages in the 

 development of this worm. A special section will be devoted to 

 the explanation of these processes. 



Skctiox iv. 



Systematic. — In this section, the trematodes found are described 

 and referred to their places in the system. For each species, a 

 brief diagnosis is given, in which the special specific characters of 

 the worm are emphasised by being printed in italics; the diagnosis 

 is followed by a fuller desci'iption of the anatomy. I should con- 

 sider this fuller description necessary, even if the worm described 

 should show no striking anatomical differences from its repre- 

 sentatives in other zoogeographical regions, because, without such 

 a description, it is often very difficult for a person knowing the 

 worm by the description only, to rightly judge what its relation- 

 ships may be. Where several species of the same genus occur 

 here, however, {e.g., Pleurogenes, etc.) there is no need to describe 

 the anatomy of more than one of these fully. The special char- 

 acters being picked out in the diagnosis, it may be taken that the 

 rest of the anatomy closely corresponds to that of the species 

 more fully described, 

 27 



