348 On the Echinoidea or Sea- Urchins. [Sess. 



red tint ; others were short, somewhat blunt, and of a deep 

 rosy -purple hue. Indeed there seemed to be enough of 

 variation from the normal type to warrant the inclusion of 

 some ill sub-species or varieties. 



Scattered about among the spines of the great majority of 

 sea-urchins are found two minute appendages, on which a few 

 words may be said. The first of these appendages are the 

 pedicellariffi or pincers, which have been known to naturalists 

 for over half-a-century, and yet their true function has only 

 lately been determined. They are, in form, small pincer-like 

 organs, scattered all over the shell, though perhaps most 

 numerous near the oral aperture. Each pedicellaria is 

 mounted on a long flexible stalk, capable of swaying to and 

 fro. in some species there are two blades in each pedi- 

 cellaria, in others four, but three seems to be the normal 

 number. These bodies are also found on the star -fishes, 

 though smaller in size ; and Miiller, who first described them, 

 regarded them as parasitic animals. Prof. Louis Agassiz at 

 one time thought they were " infant echini, which after their 

 exclusion affix themselves to the skin of their mother." 

 Again, while regarding the pedicellarias as organs of the 

 animal. Prof. A. Agassiz and others held that they were used 

 for getting rid of excrementitious particles which had become 

 entangled in the spines, and which were handed on, as it 

 were, by one pedicellaria to another until got rid of. Prof. 

 Edward Forbes said of them : " I can by no means consider 

 the question of their nature to be settled, and find myself 

 quite undecided as to whether they are organs of the Echino- 

 clermata or parasitic creatures, though inclined to the former 

 opinion." These words were written in 1841, and very little 

 of a more definite nature regarding them was discovered until 

 1881, when there was read before the Eoyal Society of 

 London a paper by Dr Eomanes, the present Eosebery lecturer, 

 and Prof. J. Cossar Ewart, — " Observations on the Locomotor 

 System of Echinodermata," — where it is affirmed that the true 

 function of the pedicellarife is at length established.^ In 1884 

 Dr Eomanes published a work entitled ' Jelly-fish, Star-fish, 

 and Sea-urchins,' in which the same conclusions regarding the 



1 This valuable paper (the " Croonian Lecture ") is now included in the 

 'Philosophical Transactions of the Royal Society of London' for 1881. 



