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type without a typical pelagic larva, the Comatulids thus offering a case 

 analogous to that of the Dendrochirote Holothurians. It may perhaps be 

 expected that typical pelagic larvae will be found to exist in some of the 

 stalked Crinoids; but till now nothing is known about that, and accord- 

 ingly the Crinoids do not contribute to the solution of the problem here 

 discussed and niust be left out of consideration for the present. 



After this summary review we may state as the result of these researches 

 that the facts hitherto brought to light are decidedly in favour 

 of the view th at th e larvae of theEchinoderms have an important 

 bearing on the classification of the adult forms. It seems a suf- 

 ficiently established fact that the larvae of closely related species are upon 

 the whole very much like one another, often hardly distinguishable, and, 

 further, that the larvae of allied genera agree in important characters, so 

 that we get groups of larvae, larval "families", "orders", corresponding to 

 the groups (families, orders) of the adult forms. Accordingly the very im- 

 portant conclusion seems justified, that when forms, which were sup- 

 posed to be nearly related, prove to have essentially different 

 larvae, these forms are not in reality nearly related^). The study 

 of the larvae will thus form a most important criterion for our classifica- 

 tion, giving, so to say, the final judgment of its true value, and we are 

 justified in stating that no classification which is in contradiction 

 to the evidence givenbythelarvaecan give an adequate expres- 

 sion of the natural relationship of the adults. — These results 

 probably apply also to other animal groups than the Echinoderms; but 

 this side of the problem will not be discussed on the present occasion. 



Although the facts already known seem to warrant the above conclu- 

 sions, I would maintain most emphatically that the present researches are 

 only to be regarded as a reconnaissance in this field. Proof is given that 

 the way entered upon is the right way, and we may be sure that further 

 researches will yield important results. But there is a long way to go. What 

 has been obtained as yet is nothing more than random samples, taken here 

 and there. It must be claimed that all the various forms should be 

 studied, and not only the genera; it will be equally important 

 to haveallthespecies within the various gen era made the object 

 of study, even though they are, apparently or really, ever so closely 

 related, and it is equally desirable that the larvae should be studied and 

 figured alive. Thus we will gradually acquire a sum of knowledge of the 

 greatest importance for reaching the end of all systematic work, the com- 

 prehension of the multitude of living forms in their natural relationship. 



Provided, of course, their embryological conditions be the same. That closely related 

 species may differ in one having typical larvae, the other having abbreviated development or 

 being viviparous, is quite a difTerent thing, and does not interfere with the above concliision. 



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