468 



The Development of the Calcareous Parts of the Lantern of 

 Aristotle in Echinus Miliaris. 

 By D. W. Devanesen, M.A. 

 (Communicated by Prof. E. W. MacBride, F.E.S. Beceived April 12, 1922.) 



[Plates 11-15.] 



CONTENTS. 



PAGE 



1. Introduction 468 



2. Method 469 



3. The Jaws 470 



4. The Epiphyses 470 



5. The Rotulse 471 



6. The Compasses 471 



7. The Teeth 472 



8. Discussion 478 



9. A comparison between Giesbrecht's account of the development of the 



urchin-tooth as revealed by its root-end in the adult and the construction 



of the same as seen in the young urchin 481 



10. Summary 483 



11. References 483 



12. Explanation of Plates 485 



1. Introduction. 



This investigation was suggested to me by Prof. E. W. MacBride, F.B.S., to 

 whom my thanks are also due for kindly placing at my disposal two meta- 

 morphosing plutei and a considerable number of young imagos of Echinus 

 miliaria, all of them fixed in absolute alcohol. 



In the year 1892, Lov^n (3) made a few observations on the embryonic 

 elements of the calcareous lantern in Goniocidaris canaliculata, a Cidarid with 

 a direct development. He also examined the same structures in two young 

 urchins which, as he himself admits, were of doubtful identity and in a state 

 of bad preservation. In the same year, Thdel (7), who was working at the 

 early development of the cake-urchin, Echinocyamus pusillus, described certain 

 early stages of the lantern in the young urchins. After these researches of 

 Loven and Thfel, it appears that no attempts have been made to study the 

 development of the lantern ossicles in greater detail and with closer scrutiny. 



It must be stated, however, that in the year 1903, in a near relative of 

 Echinus 'miliaris, viz., Echinus 'escidentus, though the origin and homology of 

 the lantern-ccelom had been investigated by Prof. MacBride (4), the calcareous 

 structures it contains remained untouched. One of the obstacles to their 

 study was the fact that non-decalcified specimens could not be sectioned 



