NORTHUMBERLAND AND DURHAM. 123 



discrimination and determination of species, some observers have 

 endeavoured to establish specific characters from the variations 

 in the form of the pedicellarise. In many instances these pecu- 

 liar organs undoubtedly afford most valuable assistance, for even 

 in the Urasters in several species those found on one are quite 

 distinct from those found on another, still they so far resemble 

 those of allied genera, that it would be unwise to base specific 

 character on such slight grounds alone, even admitting the con- 

 stancy of form which exists in the pedicellarias of certain genera 

 and species. We have still much, if not everything to learn, 

 respecting these organisms, and until we know more of their 

 character and use, we must not attempt to base specific differ- 

 ences upon a greater or smaller number of serrations upon the 

 jaw-like appendages. Specific differences, that rest upon so fine 

 a distinction, surely cannot be of much value to the student. 



Although this is scarcely the place to discuss the probable use 

 of the pedicellarias in the economy of the animal, it may never- 

 theless be desirable that they should have a brief notice. Various 

 have been the conjectures recorded upon this puzzling question. 

 Some naturalists have assigned to them a similar office to that 

 of the "avicularia" or "birds-heads" of the Polyzoa, "being 

 intended to seize minute animals and to hold them till they die 

 and decompose as baits to attract clouds of infusoria, which, 

 multiplying in the vicinity of the urchin, may afford it an abun- 

 dant supply of food."* This is scarcely likely, for it is doubtful 

 whether these animals prey upon infusoria ; if they do, where 

 would be the necessity for the powerful dental apparatus with 

 which several of them are provided ? And, further than this, 

 as recorded in this catalogue, the writer has dredged numbers 

 of urchins (E. esculentus and E. neglectus) on the coast of North- 

 umberland ; these, on being cleaned, were found to be filled 

 with small particles of marine alga? which had been "grazed" 

 from a weedy bottom, where the animals had congregated in 

 immense numbers. Again, those who are disposed to favour 

 Mr. Gosse's idea, might be asked to account for the absence of 



* Gosse. Evenings at the Microscope, p. 346. 



