xo. 7 



PROTECTIVE ADAPTATIONS McATEE II 



Number of identifications, 2 ; percentage of identifications among 

 those of all animals, .0008 ; percentage of species in this phylum 

 among the whole number of animal species known, .8028. 



Discussion. — Information at hand seems to indicate that sponges 

 are used very little as food by other animals ; sea-urchins, marine 

 worms, amphipods, and mollusks, however, are recorded as predators. 

 Fresh water sponges are eaten to some extent by fishes. Whether 

 this is credited to their " protective adaptations " is of little moment 

 as the fact remains that sponges do not multiply excessively nor 

 overrun the earth as forms that lack enemies are in theory supposed 

 to do. 



Sponges have bright and varied colors and one case of mimicry has 

 been pointed out.' If it be true as apparent from observations thus 

 far, that they have few or no enemies, natural selection can not be 

 advanced as an explanation of their color phenomena. If sponges 

 without enemies have adaptations of the same character as other 

 groups with numerous enemies, it would seem evident that selection 

 by predatory animals has no necessary connection with the adaptations. 



COELENTERATA (HYDRAS, JELLYFISHES, SEA-ANEMONES) 



Protective adaptations. — Some coelenterates have a chitinous cuti- 

 cle, others have a calcareous skeleton, and many of them have nema- 

 tocysts or stinging cells. Numbers of them are brilliantly colored or 

 phosphorescent but it must be noted also that many are transparent 

 or nearly so. showing that possession of protective devices (as the 

 nematocysts) is not always accompanied by the development of 

 " warning colors." 



Bird enemies. — The Coelenterata most often found in bird stomachs 

 are the Hydrozoa (such as Ahietinaria, Scrtularclla, and Thuiaria). 

 They have been identified 113 times from the stomachs of 13 species 

 of ducks, 2 of gulls, and one each of nuu'rc, murrelet, and shearwater. 

 Sea-anemones {Anthopleura, Aidactiuia) have been identified four 

 times from stomachs of a scoter, an eider, an oyster-catcher, and a 

 gull, Alcyonaria from two ducks, and coral from one. 



Number of identifications, 122; percentage of identifications aiuong 

 those of all animals, .0514 ; percentage of species in this phylum among 

 the whole number of animal species known, .8028. 



Other enemies. — Hydroids are eaten by marine worms, by sea- 

 urchins and sea-anemones, and also bv fishes, as the cod, haddock. 



* Mcintosh. W. C., The coloration of marine animals. Ann. Mag. N-'t- IH'^t. 

 7th ser., vol. 7, p. 223, Mar., 1901. 



