152 Prof. M'Intosli's Notes Jrom 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 otlierwise 

 identical. In the same way some on the same masses from 

 the North Sea had an operculam as an exception, and 

 though Sars described the Norwej>;ian representative as 

 having an operculum, others lately examined from the same 

 region had none. The varying size and shape of the oper- 

 culum, and tlie reinarkal)le susceptit)ility of the branchiae 

 themselves to change in filaments, pinnae, terminal region, 

 and glands, suggest the instalnlity of a character derived 

 from the operculum in Filograna. 



The tips of the filaments, like the branchiae 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' 

 Nea|)olitan tj'pe — Salmacina cedijicatrix, — in which the non- 

 ciliated tip forms an elongated sausage-like process, though 

 it is probably flattened. No operculum is developed 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 

 Claparede. De Quatrefages supposed that in Huxley's 

 Protida 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 ojjercula 

 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 

 piocesses in every instance, and in several the expansion 

 passed down the filament for some distance. Others showed 

 siuidar enlargements at the tips of the brauchiee and no 

 opercula, and a third series presented a minute flattened or 

 slightly saucer-shaped operculum on each dorsal filament 

 which could 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 



