152 ~ Prof. M‘Intosh’s Notes from the 
swarms of those devoid of opercula from the neighbourhood 
of the Bell Rock a few were found with them. That fact: 
would seem to dispose of the importance of the operculum: 
as a specific distinction, for the animals are otherwise 
identical. In the same way some on the same masses from’ 
the North Sea had an operculum as an exception, and 
though Sars described the Norwegian representative as 
having an operculum, others lately eerancd from the same 
region had none. The varying size and shape of the oper- 
culum, and the remarkable susceptibility of the branchivz 
themselves to change in filaments, pinne, terminal region, 
and glands, sugg jean the instability of a character denivell 
from the operculum in Filograna. 
The tips of the filaments, like the branchie as a whole, 
present equal response to external or internal influences.: 
The maximum change, independently of the formation of an 
operculum, so far as at present known, is observed in the: 
Neapolitan type—Salmacina edificatrix,—in which the non- 
ciliated tip forms an elongated sausage- ‘like process, though 
it is probably flattened. No operculum is developed i in’ this 
type. Similar, though smaller, enlargements take place in 
the Plymouth and southern non-opercular forms, and which, 
though not specially noted by Huxley, were alluded to by 
Claparéde. De Quatrefages supposed that in Huxiey’s 
Protula dysteri these enlargements corresponded to the 
ovigerous opercula of the Spirorbids 
In those with opercula from the French coast, the Channel 
Islands, Shetland, and Norway, no enlargement of the ter- 
minal region of the filaments, as a rule, was present. Only 
in certain examples from the North Sea modified opercula 
and terminal enlargements of the filaments occurred, Thus 
in an example with eight pairs of anterior bristles one dorsal 
filament had a somewhat thick terminal process, rather 
abruptly bevelled on one side, whilst the other filament had 
advanced a stage further—the clavate tip being unequally 
bevelled and hollowed so as to form a rudimentary operculum. 
On the same ground (455 metres) another had the tips of 
the filaments more irregularly enlarged as flattened lobate 
processes in every instance, and in several the expansion 
passed down the filament for some distance. Others showed 
similar enlargements at the tips of the branchiz and no 
opercula, and a third series presented a minute flattened or 
shghtly saucer-shaped operculum on each dorsal filament 
which couid have been of little use as a protection. At 
other stations the forms of the opercula varied from the thin 
translucent, more or less circular or hoof-shaped cup to a 
lee ly 
A ig ee A ei! 
