114 The Irish Naturalist. May, 



traces of having reached the adult stage. I speak here with 

 some hesitation, because I have described and figured the 

 organs of reproduction, and made note of eggs in the ovisac 

 of the Aster Worm. But this fact would not weaken my theory 

 since we know that the larvae of some gnats lay eggs, and it 

 is, therefore, not unreasonable to allow that the larval forms 

 of annelids ma}^ do the same. We have, again, the analogy 

 of the Mites to help us. The Etichai^is mite, for example, 

 develops from a creature with six legs in the larval stage, to 

 one with eight in the imago. What is there, then, in the nature 

 of things to prevent a worm from developing in the same way ? 

 If this theor}^ of evolution through a larva be accepted, it will 

 throw light on a number of points in the anatomy and life- 

 history of some species of worms which are at present obscure. 

 It might further aid us in understanding and reconciling the 

 descriptions of some of the earlier naturalists, who, studying the 

 larval and imago forms at the same time, tell us that the setae 

 and certain organs vary in number, size, position, and other 

 details in the different specimens. 



To me, therefore, it seems that we have here a capital 

 working hypothesis, and one cannot but wonder that some of 

 the man}^ admirable workers among the annelids have not hit 

 upon the theory before. If we grant that worms may pass 

 through different stages of development, we may have a 

 possible clue to the meaning of Ltc7nbriculus, for example, 

 which seems very clearly to be a larval form. It has never yet 

 been found in this country in a mature form, though Vejdovsky 

 reports adult forms from some Continental habitat. More- 

 over, a new light will be thrown upon the position which 

 worms hold in the scale of being. We shall see them to be 

 arrested forms of life, which, though they have themselves 

 been evolved from lower larval forms, have yet been unable to 

 get beyond the grade of larvae. When, too, we remember 

 that larvae moult, we shall not find it difiicult to believe that 

 if the Aster Worm does not produce another form of worm by 

 an alternation of generations, it nia}^ do so by shedding its 

 skin, and at the same time assuming a different number of 

 setae. I shall hail with delight any facts which enable us 

 to solve one of the most interesting problems which the study 

 of annelids has yet suggested. 



