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The Locomotor Function of the Lantern in Echinus, tvith Obser- 

 vations on other Allied Lantern Activities. 

 By J. F. Gemmill, M.A., M.D., D.Sc, F.Z.S., Lecturer in Embryology, Glasgow 

 University, and in Zoology, Training College, Glasgow. 



(Communicated by Dr. E. W. MacBride, F.B.S. Eeceived January 17, — 

 Eead February 29, 1912.) 



CONTENTS 



I. Locomotion out of Water .... 



II. Locomotion under Water .... 



III. Relation to other Activities . 



TV. Summary 



I. Out of Water. 



Thirty years ago, in a paper to the Eoyal Society of London,* Eomanes and 

 Ewart pointed out that a sea-urchin uses its lantern in progression out of 

 water, and gave an account of the manner in which the lantern acts. This 

 account, however, seems to have been passed over completely, since there is 

 no mention of it in the later book of Eomanes, 1 Jellyfish, Starfish, and 

 Sea-urchins,' London, 1885, nor is it referred to in any of the general or 

 special works dealing with Echinoderms that I have come across.f What 

 one gathers from these sources, when they refer to the point at all, is that, 

 out of water, sea-urchins are able to travel for short distances by using their 

 spines as so many stilts, with the help of which they can pole their way 

 along slowly and with difficulty, the motive power coming from the muscular 

 collars at the bases of the spines. The writer has to confess that he was 

 entirely ignorant of the account given by Eomanes and Ewart in the paper 

 above referred to, until after the whole of the following observations on 

 locomotion had been made. 



In view of the circumstance detailed above, and also as I have been able to 

 obtain records of the action by a number of methods and to add much 

 collateral information, it may not be amiss if a full and independent 

 description be here given, all the more since that of the two authors named 



* " Observations on the Locomotor System of Echinodei mata," ' Phil. Trans.,' London, 

 1881, pt. 3, pp. 829—855. 



t E.g., Bronn's ' Klassen u. Ordnungen,' Leipzig, 1904, vol. 2, p. 4 ; ' Cambridge Natural 

 History,' vol. 1 ; ' Treatise of Zoology,' ed. by E. Eay Lankester, London, 1900, pt. 3 ; 

 Delage et Herouard's ' Traite de Zoologie Concrete,' Paris. 1903, vol. 3 ; L.M.B.C. Memoir 

 on Echinus, by H. C. Chad wick, Liverpool, 1900. 



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