123 



to shed the eggs. The fertilization follows immediately, and the eggs 

 develop normally. In this way I have succeeded in obtaining the larvae 

 of several species, and also other investigators have succeeded in the same 

 way (Apostolides, Fewkes, Grave). 



But even if one succeeds in obtaining the young larva', tin- difficulties 

 are not at an end. The Diatom cultures, which are used so successfully 

 for feeding the Echinoid-, Asteroid- and Ilolothurioid-larvae, are not readily 

 accepted by the Ophiuroid-larva? and apparently do not form a proper 

 food for them. It is very probable that cultures of different Flagellates 

 will prove to give good results, and this should of course be tried on future 

 occasions. But this has not yet been done. The results obtained till now, 

 those of my own researches included, are thus comparatively poor, and 

 especially quite insufficient with regard to the main object of the present 

 researches, the study of the interrelation between the larva? and the adults 

 and their bearing on a natural classification. 



There is also another way in which it is possible to trace the larva? to 

 their parental origin, viz. to rear the Ophiurid from the larva. When taken 

 from the plankton in so far advanced a stage of metamorphosis that 

 feeding has ceased, the larvae, if unhurt and carefully transported to 

 separate dishes, will go on metamorphosing. If then suitable conditions 

 are given the young Ophiurid, it is possible to rear it, till it has grown 

 to a size which allows identification. This was done recently by the author 

 with Amphiura filiformis 1 ). There is no doubt that we may obtain im- 

 portant results in this way owing to the fortunate circumstance that the 

 main specific characters of the larva? remain unaltered till metamorphosis 

 is almost complete, so that it is very well possible to identify first the 

 larva? and then later on the Ophiurid developing from it and thus to 

 establish their genetic relation. 



Till now, however, both methods have yielded so few results That not 

 much can be concluded therefrom, and the question whether definite types 

 of larva? corresponding to the larger groups of Ophiurids can be recognized 

 does not get a definite solution from the knowledge thus acquired; indeed, 

 the impression conveyed by the facts hitherto made known rather comes 

 to this that there are no such natural groups among the Ophiiirid-larva-. 



The Ophiurid larva? are very easily preserved in a fairly good condition, 

 in general far better than the Echinoid-larvae ; even in usual plankton 

 samples, preserved simply in alcohol, Ophiuroid-larva' may be found in 

 very good, or at least in fully recognizable stale. On account of this for- 

 tunate circumstance I have been able to collect a very large material of 



1 ) Th. Mortensen. Notes on the development anil the larval forms of some Scandinavian 

 Echinoderms. Vid. Medd. Vol. 71. 1920. p. 138. 



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