420 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



it writes on the paper; just as each can be distinguished by certain 

 anatomical characteristics. 4 



II 



I turn from the polychaetes to a group of animals that has a wider 

 appeal and is very much in the limelight nowadays — the birds. I am 

 going to suggest that much of what I have said about worms is true 

 in principle of birds too. 



At this stage in the argument, I am reminded of a proverb that the 

 shrewd old Russian peasants used to say in the days before the revolu- 

 tion. They would peck at their fields with primitive tools, as their 

 fathers and grandfathers and great-grandfathers had done before 

 them ; and when one suggested that more modern methods might in- 

 crease productivity, they would shake their heads and say : "If you 

 make your strides too great, you tear the seat of your pants." 



The step from worms to birds is a long one. I encourage myself 

 with the thought that all animals, however different they may ap- 

 pear, are variations on a common theme. It is, of course, the aim of 

 the comparative method to find out how much is variation and how 

 much is theme. 



Probably nearly all of us have been irritated at one time or another 

 by the insistence with which our feathered songsters repeat their 



4 The "mood changes" are strikingly shown by Chaetopterus variopedatus, 

 which has several very characteristic and clearly contrasted alternative ac- 

 tivity patterns. The statement about the Sabellidae is based on published rec- 

 ords got from Sabclla spallanzanii at Naples and Sabella pavonina at Plymouth, 

 and unpublished ones from Branchiomma vesiculosum at Plymouth and 

 Schizobranchia insignis at Friday Harbor, the latter with the assistance of LeRoy 

 B. Nydegger. In Myxicola infundibulum, which is referred on anatomical 

 grounds to a separate subfamily, no water is driven through the tube, although 

 there are other characteristic activity patterns. 



Comparison of the two Sabella species is interesting. The tubes are found, 

 either attached to such submerged objects as rocks, piles and buoys, or with their 

 lower ends embedded in the material of the sea bottom. The ecological pref- 

 erence of the two species are not quite the same ; 8. spallanzanii occurs attached 

 to submerged objects or embedded in coarse sand, while 8. pavonina — though it 

 also can occur in these situations — is especially frequent in muddy sand or in 

 mud. The spontaneous irrigation patterns of the former involve the propulsion 

 of water in both directions in turn, those of the latter in a tailward direction 

 only. If 8. pavonina draws an irritating substance into its tube with its water 

 current, it can at once reverse the current and thereby take rejection action ; it 

 is therefore capable of reversal though it never reverses except in response to 

 such occasional crises ; the normal restriction of its behavior to tailward irriga- 

 tion may be correlated with its habit of colonizing muddy situations, since a 

 headward current, in such situations, would tend to draw in mud and clog the 

 tube. 



This is only one example of the fact that an inherent activity pattern can be 

 adaptively modified, just as an anatomical pattern can. 



