POLYCH AT LARVA. 641 
Mecznikow describe and figure a similar larva, but refer 
it to the Spioniform genus Polydora (1869: p. 175; PI. 
XII., fig. 3: see above p. 641). Willemoes-Suhm figures 
another such larva (1871: Pl. XXXI_., fig. 11), but does 
not identify or describe it. 
CONCLUSION. 
In the present limited state of our knowledge of 
Polychaet larvae it would be futile to attempt to give a 
diagnosis of the larval characteristics of the different 
famihes and genera of Polychaets. In the vast majority 
of genera the early stages are quite unknown, and where 
anything zs known of them it is confined to a very small 
proportion of the known adult species. A table for the 
identification of the above described species from Port 
Erin, however, will form a convenient summary of their 
most useful characters for systematic purposes; and 
wherever possible the particular characters given will be 
those that at present seem most likely to be of general 
appleation. 
As I have only been able to describe the trochophore 
stage in any detail in two of these larvae, and as the 
latest pelagic stages of the Nereidiformia are characterised 
chiefly by the characters of the adult, the following table 
will deal specially with the metatrochophore stage, or 
in the Spioniformia with this and the nectosoma stage ; 
references to any special characters of the other known 
stages will be enclosed in brackets. 
It should be noted that many of the characteristics 
mentioned are intimately connected, or even identical 
with those of the adult worm, and therefore cannot be 
used as embryological evidence, independent of adult 
structure, for or against any particular scheme of 
Polychaet classification. 
