328 
FISH MYXOSPORIDIA FROM PLYMOUTH. 
By J. S. DUNKERLY, B.Sc. (Bond.). 
Natural History Department , Glasgow University. 
(With 6 Text-figs.) 
During the summer of 1914 and during the months January to April, 1920, 
I have been able to investigate the Myxosporidian parasites of fish occurring 
at Plymouth, and I am glad to take this opportunity of thanking the Ray 
Lankester Trustees for their grant in aid of this research, and also to express 
my gratitude for the very valuable and kind assistance afforded me by the 
Director, Dr E. J. Allen, and staff of the Marine Biological Station at Plymouth, 
where the researches were carried out. The assistant Mr Smith helped me very 
considerably in the identification of the fish examined. * 
I have been unable as yet to work out the material fully, especially the 
interesting developmental stages, and as it may be some time before I am able 
to do this, it may be useful to give a list of the forms found in fish met with 
at Plymouth, and to describe briefly some new forms. 
Quite a number of new hosts were found and it is a matter of difficulty 
at present to decide whether a parasite found in a new host is a new species 
or not. The same difficulty occurs of course in other groups of parasites, 
notably Trematoda and Anoplura, and while some species are certainly found 
in many different hosts, others apparently are very restricted in their choice 
of hosts, even when abundant opportunities occur for infection. In this paper 
a very conservative attitude has been adopted with regard to possible new 
species. When a form has been found with spores which agreed with a pub¬ 
lished description, the parasite has been given the name of the earlier described 
species, although found in a different host. The plasmodial stages do not show 
sufficiently clear distinctions to serve for specific or even generic character¬ 
istics, except in rare cases like the pigmented plasmodium of Chloromyxum. 
Some of the forms described under pre-existing names may be found 
subsequently to be distinct species, but with our present defective knowledge 
of life histories in this group it is better to describe the same species as occurring 
in different hosts rather than create new specific names which might have to 
be abandoned later. Some species like Chloromyxum leydigi have been re¬ 
corded already from many different hosts, and it will be seen that a form 
indistinguishable from Myxidium incurvatum is here recorded from several 
different hosts. On the other hand, there appear to be some species which 
