THE DEVELOPMENT OF OPHIOTHRIX FEAGILIS. 



557 



The Development of Ophiothrix fragilis. 



By 

 E. W. I?IacBri<le, WI.A., D.Sc, F.R.S., 

 Professor of Zoology in McGill University, Montreal. 



With Plates 31—36, and 4 Text-figures. 



Contents. 



PAGE 



Introduction ..... 557 



Historical Sketch . . . . .558 



Material and Methods .... 567 



Normal and Abnormal Development . . . 570 



The Development of the Full-grown Larva . . 575 



Metamorphosis of the Larva into the Brittle-star . . 580 

 Comparison with Development in other Classes of Echino- 



dermata . . . . . . 590 



Summary and Conclusion .... 596 



Inteoduction. 



The present work, wliich lias occupied my attention for the 

 last four years, was begun with the object of extending to 

 other classes of Echinoderms the researches which I had 

 already made on the development of Asteroidea (18) and 

 Echinoidea (19). It has proved to be a task of extraordinary 

 difficulty owing to the minute and refractory character of the 

 larvae of Ophiuroidea. Nevertheless, the results obtained 

 will, I think, bear fair comparison with those which I have 

 already published concerning the development of Asteroidea 

 and Echinoidea, whilst a number of new and unexpected 

 facts have disclosed themselves which possess interest for a 



