638 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIEVY. 
greatly reduced—possibly absent; the anal ridge, 
however, is still fully developed and covered with black 
pigment spots. No setae, except the paleae, can be seen 
in this specimen, but no doubt this is due to their being 
placed, in the mounted and rather deeply stained 
specimen, so as to occupy a position above the body, or to 
their having been shed during fixation; I have therefore 
inserted them in the figure in the position they occupy in 
larvae during the quiescent period cm before 
metamorphosis. 
During my visit to Port Erin in 1908 I had the good 
fortune to see something of the metamorphosis in progress 
in a living larva. From a plankton collection taken on 
August 1, a number of Polychaet larvae were picked out 
as usual, and placed in fresh sea water in a crystallising 
dish from which they were taken for examination one by 
one. Amongst these was an advanced Metatrochophore 
of Pectinaria, which towards the end of the morning pre- 
sented a slightly abnormal appearance, giving me the 
impression (when seen under a low power of the micro- 
scope) that it would not live much longer, and would 
even then be of no use for detailed examination; this 
was not at all surprising, for the larvae usually showed 
such signs of deterioration after five or six hours, and 
even sooner. However, the larva was allowed to remain 
in the crystallising dish, and when I again saw it under 
the microscope, after an interval of about half an hour, I 
found that its previous abnormal appearance had been 
due to the fact that it had been in an early stage of the 
metamorphosis which it had now almost completed. The 
metamorphosis was, indeed, so far advanced that I decided 
to fix the larva at once, and so only gave it a cursory 
examination with the low power during life. This larva 
is shown in Pl. IV., fig. 45, from which it will be seen 
