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NO. 7 PROTECTIVl-: ADAPTATIONS- 



Idciitifu'iifioiis of Chordula 



Number of 



Class identifications 



Ui'ochorda 5 



Pisces 4,923 



Amphibia 997 



Reptilia 695 



Aves 3-555 



Mammalia 3.15^ 



The urochordates listed are ascidians, in three cases being identified 

 as Boltenia ovifera. While the identifications of urochords is far 

 from proportional to the frequency of these animals, the result is 

 only what would be expected in view of their strictly marine and 

 chiefly submerged habitat in which they are exposed to the attacks of 

 only a very small proportion of our birds. It may be noted here that 

 tunicates have numerous enemies, however, among fishes which take 

 the pelagic and both simple and colonial fixed ascidians. It is on 

 record that these animals are not uncommon in the stomachs of cod 

 and haddock, and they have been found also in herring, flatfishes, 

 tilefish, cunner, scup, the great sunfish (Alola), and a number of 

 other fishes. They are taken also by sea-anemones and sea-urchins. 



Omitting the Urochorda and figuring frequency indices from the 

 fairly well known numbers ' of .Vorth American species in the various 

 classes we obtain the following table : 



Identifications of Vcrtcbrata 



In this as in other cases wc clearly observe the tendency for losses 

 to predators to correspond to the extent and abundance of a group. 

 In fishes the largest class are preyed upon the most, but less than their 



'Counts derived from stand;-.rd works on tlic various classes, as UDted later in 

 connection with the tabulations by classes. 

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