POLYCHAT LARVAL. 577 
actively in motion. Though only approximate, these 
figures will, I think, convey a better idea of the relative 
lengths of various cilia than could be obtained from the 
constant use of such vague comparative terms as “ long,” 
~* medium,” and ‘ short.” 
This paper can only claim to give a preliminary 
account of the larvae it describes; as, however, many of 
these larvae have not been described before, and as no 
systematic account of British Polychaet larvae has yet 
been attempted, even for such a limited area and part 
of the year as Port Erin Bay during the month of July, 
it seems advisable to publish it in its present form, and 
to leave the obvious gaps in some of the accounts to be 
filled in as opportunity presents itself. I have 
endeavoured by references to previous work on the 
subject to indicate briefly the nature and extent of the 
variability of larvae within each of the families dealt 
with, and their complete life-histories as far as they are 
at present known. 
I should like to express my thanks to Prof. Hickson 
for nominating me to the Manchester University table in 
the laboratory at Port Erin during the times I was: 
collecting the material described below; also to Prof. 
Herdman for very kindly supplying me with samples of 
the plankton he collected from his steam-yacht “ Lady- 
bird * in the large “ shear-net,”” from which it was hoped 
—unfortunately in vain—that there might be obtained 
later stages of Polychaet larvae than those caught in the 
ordinary small tow-nets; and finally to Mr. Chadwick for 
many valuable suggestions, and ready help in many ways. 
