5G0 



PEDICELLAKLE AND TEETH OF ECHINUS. 



also to find that the same structure presents itself in the curious 

 Pedicellarice (forceps-like bodies mounted on long stalks), which 

 are found on the surface of many Echinida, and the nature of which 

 was formerly a source of much perplexity to Naturalists, some main- 

 taining that they are Parasites, whilst others considered them as 

 proper appendages of the Echinus itself. The complete conformity 



Fig. 290. 



Spines of Spatangus. 



which exists between the structure of their Skeleton and that of 

 the animal to which they are attached, removes all reasonable doubt 

 of their being truly appendages to it, as observation of their actions 

 in the living state would indicate. * 



433. Another example of the same structure is found in the 

 peculiar framework of Plates which surrounds the interior of the 

 Oral orifice of the shell, and which includes the five Teeth that may 

 often be seen projecting externally through that orifice ; the whole 

 forming what is known as the ' Lantern of Aristotle.' The texture 

 of the Plates or Jaws resembles that of the Shell in every respect, 

 save that the network is more open ; but that of the Teeth differs 

 from it so widely, as to have been likened to that of the Bone and 

 Dentine of Vertebrate animals. The careful investigations of Mr. 

 James Salter, f however, have fully demonstrated that the appear- 

 ances which have suggested this comparison are to be otherwise 

 explained ; the plan of structure of the Tooth being essentially the 

 same as that of the Shell, although greatly modified in its working- 



* See Dr. W. B. Herapath in "Quart. Journ. of Microsc. Science,'' 

 Vol. v., N.S. (1865), p. 17/). 



t See Ms Memoir ' On the Structure and Growth of the Tooth of Echi- 

 nus, in " Philos. Transact." for 1861. 



