On the Development of the Trematoda 



A PAPER READ BY G. DOWKER, F.G.S. 



My excuse for bringing this subject forward this evening in place 

 of the continuation of my former paper on Coast Changes is, that I 

 have lately met with an extraordinary number of infusoria of a 

 peculiar type, and exactly similar to another such swarm I found 

 the year 1866, and that they are so difficult to keep alive any 

 length of time. As a preface to my subject, I will give you the 

 history of the animals I have met with. In the year 1866 and 

 in the month of June that year, I observed a very peculiar 

 appearance in one of my ponds. It was hot sultry weather. The 

 pond in question had water lilies and aquatic plants in it, and I 

 observed one evening all the vegetation covered with an opaque 

 yellow substance, as if flower of sulphur in great quantity had 

 been thrown into the pond. On examination, these proved to 

 be innumerable infusoria, of leech-like form, which adhered 

 together on the plants like swarms of bees. Being unable to 

 determine to what class these animals belonged, I sent living 

 specimens to Dr. Carpenter, and received in reply two letters, 

 dated June 25, 1866, and July 30 of the same year. In the latter 

 he states, "Your last little bottle afforded me the opportunity 

 of carefully studying it ; and I have also, finding it new to me, 

 shown it to Professor Huxley. Its general characters are those 

 of the turbellarian worms (to which the planaria belong), but its 

 internal organization is so imperfect, and its diffluence so ready, 

 that we are disposed to think it a larval form of some higher 

 creature. Its nearest affinities seem to be to opalina, which is a 

 parasitic worm of about the same grade of organization, and 

 perhaps also a larval form." These infusoria I examined under 

 the microscope, and made measurements and drawings of them, 

 which I have by me. They appeared for some time in the pond 

 before mentioned, but gradually disappeared, and have not 

 appeared again since till this year — at least in such numbers, as 

 I have carefully looked for them. They usually dispersed in the 

 water in the day-time, but towards evening collected in the 

 curious clusters or festoons on the weeds. There was no 

 difficulty in collecting thousands of them on such occasions, 

 uncontaminated with any other animalcule ; and I kept numbers 

 of them in bottles holding at least a quart of water, but I could 

 not succeed in keeping them alive any length of time — they all 

 shrank up into an oval egg-shape body and sank to the bottom 

 of the vessel. 



I will now give a description of these animalcule. They were 

 about a fortieth of an inch in length, flat and ribbon-like, 

 ciliated at the edges. They proceeded through the water with a 



