On the Development of some British Echinoderms. 



By 

 Dr. Th. Mortensen, Copenhagen. 



With Figures 1-15 in the Text. 



For several years I have felt the desire of going to Plymouth in order to 

 gain practical knowledge of the excellent methods for rearing pelagic 

 larvae of marine animals, which have been worked out there, especially 

 by the Director of the Marine Biological Laboratory, Dr. E. J. Allen. 

 I was therefore very glad to receive last year an invitation from Dr. 

 Allen to come and stay some time at his laboratory, and having got a 

 grant for this purpose from the Carlsberg Fund and from the Danish 

 Government, I had at length the desired opportunity. 



The time I spent in Plymouth — from June 10th to July 15th this 

 summer (1913) — was long enough for learning the methods, but, unfortu- 

 nately, too short for having the full profit of my rearings, because several 

 of the larvae take a longer time to reach their full size and still more to 

 pass through metamorphosis. However, the results attained are not 

 unimportant. 



No less than six different species of Echinoderms were reared to a more 

 or less advanced stage of development, according to the date at which 

 fertilization could be undertaken, and according to the rate of growth of 

 the different larval forms. These six species are : Asterias cjlacialis, 

 Luidia ciliaris, Ophiactis Balli, Ophiocoma nigra, Spatangus purpureus, 

 and Holothuria nigra. Fertilization of Echinocardium flavescens was also 

 undertaken, but unfortunately the whole culture was destroyed by an 

 accident, and no material was got later on of the species. Some other 

 forms, the development of which I wanted likewise to study, e.g. Echino- 

 cardium pennatifidmn, AmpJiiura {Ophiocnida) brachiata, Ophiopsila 

 ■aranea, were not ripe at that time or sufficient material could not be got. 



The main purpose of these studies on the larval development of differ- 

 ent Echinoderms — which I hope to have the opportunity of continuing 

 during a planned voyage to the Pacific — is to find the characteristic 

 features of Ihe larval forms and to see if the larvae have any bearing on the 



NEW SERIES. — VOL. X. NO. 1. XOVEMBER, 1913. 



