'28S ON SOMK TRKMATODK PARASITES OF AUSTRALIAN FROGS, 



One of the difficulties in the wa}^ of the formation of natural 

 genera, as "muster" groups of species, was the large number of 

 species standing isolated without any ajjparent generic com- 

 panions. One of the chief reasons foi- the apparent isolation of 

 such species was, of course, as so clearly declared by Looss, that 

 the species in question was not a real species, but a whole group 

 of species, the differentiating characters of which had escaped 

 observation; but, in many cases at least, the reason seems to me 

 to have l)een that their generic companions had not yet been dis- 

 covered. This difficulty is now being rapidly overcome by the 

 discovery and description of trematodes from, for the most part, 

 similar sources in other zoogeographical regions. On this subject, 

 I shall have more to say in a later section of this woi'k. The 

 Trematodes are a very old group of animals and, owing to the 

 conditions under which their parasitic life is passed, they 

 experience e\olutionary changes much more slowly than their 

 hosts, so that we find closely related species of the same genus of 

 these worms living in hosts which are not only now widely sepa- 

 rated geographically, but which have diverged fi^om their parent- 

 stock even beyond the limits of natural genera. 



The present-day, more satisfactory state of our knowledge of 

 the classification of the Malacocotylea owes much to the recent 

 work of Looss, Braun, Liihe and Odhner, who, within the last 

 few years, have defined many natural genera, subfamilies, and 

 families of this group. 



The Trematodes of American frogs have been described, and 

 their relationships pointed out chiefly by Stafford(85-91), and 

 Pratt(75-77), and to a less extent by Bensley(3), Nickerson(66), 

 and Seeley(81); while the Asiatic forms have been investigated 

 by Liihe(60), and Klein(38). 



Section ii. 



Material Inventiyated. — The first Trematodes from frogs that 

 came into my possession were given me by Dr. J. P. Hill, who 

 was, at that time, on the staff of the Sydney University, but who, 

 soon afterwards, went to London to take up the duties of the 

 Jodrell Chair of Zoology at University College. In the follow- 



