213 



Turning to the Ophiurid-larvae we find matters much less clear than 

 is the case with the Echinoid-larvse. In fact, our previous knowledge would 

 hardly seem to warrant any other conclusion than this, that these larvae 

 form a rather chaotic assemblage; thus e. g. the larvae of forms so closely 

 related as Ophiura affinis, albida and texturata are so different, that they 

 would rather seem to belong to different famihes than to closely related 

 species. The present researches, however, tend to prove that matters do 

 not stand quite as badly. 



It may be regarded as an established fact that within the genus Ophio- 

 thrix the larvae are of a very uniform character, so uniform, indeed, that 

 it is in many cases impossible to distinguish the various larval species. 

 Whether this type is peculiar to the whole family of the Ophiothrichidae, 

 and not to the genus Ophiothrix alone, remains to be proved. But in any 

 case we have here a distinct larval type common to the very numerous 

 species within this genus, and there is not the slightest reason to believe 

 that the larvae of any of these species should prove to differ markedly from 

 the common type. This is then in perfect accordance with the legitimate 

 claim, that nearly related forms should agree in regard to their larval 

 characters. 



Another conspicuous case is afforded by the Op/izoco/na-larvae. The four 

 (or five) larvae hitherto known are so closely alike that it may be safely 

 stated that there is a distinct larval -type of this genus, characterized 

 through the transformation of the central part of the body skeleton into 

 a sort of link, and through the existence of vibratile lobes. Whether this 

 larval type is peculiar also to the family Ophiocomidae remains uncertain. 



The study of the great variety of Ophiuroid larvae of unknown origin 

 has disclosed the important fact that also among these larvae several 

 distinctly characterized types may be distinguished, each comprising seve- 

 ral species. After the analogy of the genera Ophiothrix and Ophiocoma it 

 may very reasonably be concluded that these types represent various 

 genera, the larvae of the different species within these genera being upon 

 the whole closely alike, as should be claimed upon the theory of the classi- 

 ficatory value of the larvae. Such larval types are especially Ophiopluteus 

 undulatus, 0. arcifer, 0. pusillus, 0. serratus-bimaculatus. 



It is then hardly to be denied that definite proof has been given that, 

 also within the Ophiuroids, the larvae of closely related species 

 are in general similar, agreeing in their main characters. The 

 conclusion to be derived from this fact must needs be this that the con- 

 spicuous difference between the larvae of Ophiura albida, affinis and texturata 

 proves these forms not to be so very closely related, in spite of the fact 



