300 MISCELLANEOUS OBJECTIONS TO THE [Chap. VII. 



moveable. I wish I had space here to give a fuller 

 abstract of Mr. Agassiz's interesting observations on the 

 development of the pedicellarise.. All possible grada- 

 tions, as he adds, may likewise be found between the pedi- 

 cellarise of the star-fishes and the hooks of the Ophiurians, 

 another group of the Echinodermata ; and again between 

 the pedicellariaB of sea-urchins and the anchors of the 

 Holothurise, also belonging to the same great class. 



Certain compound animals, or zoophytes as they have 

 been termed, namely the Polyzoa, are provided with 

 curious organs called avicularia. These differ much in 

 structure in the different species. In their most perfect 

 condition, they curiously resemble the head and beak of 

 a vulture in miniature, seated on a neck and capable of 

 movement, as is likewise the lower jaw or mandible. 

 In one species observed by me all the avicularia on the 

 same branch often moved simultaneously backwards and 

 forwards, with the lower jaw widely open, through an 

 angle of about 90°, in the course of five seconds ; and 

 their movement caused the whole polyzoary to tremble. 

 "When the jaws are touched with a needle they seize it 

 so firmly that the branch can thus be shaken. 



Mr. Mivart adduces this case, chiefly on account of 

 the supposed difficulty of organs, namely the avicularia 

 of the Polyzoa and the pedicellariae of the Echinodermata, 

 which he considers as " essentially similar," having been 

 developed through natural selection in widely distinct 

 divisions of the animal kingdom. But, as far as struc- 

 ture is concerned, I can see no similarity between tridac- 

 tvle pedieellarke and avicularia. The latter resemble 

 somewhat more closely the chelae or pincers of Crusta- 

 ceans ; and Mr. Mivart might have adduced with equal 



