Enci/slment ty"/Koluso:na. 17 



knowledge of the cocoons of the Oligochaita he ubservc.i \vit!i 

 regard to ^olosoma, " Aut" die Schilderung der vermeint- 

 iichen Cocons von u^olosoma wie sie seinerzeit Maggi 

 g-egeben liat, verzichte ich einzugehen, da es hier diirchaiH 

 unklar bleibt, ob er tliatsachlich Cocoas, oder encystirte 

 Wiirnier gesehen hat." I am not certain whether Prof. 

 Vcjdovsky is speaking here of liis own knowledge or is 

 merely argniiig from Maggi's figures ; be that as it may, I 

 believe that Vejdovsky's suggestion of encystment is the 

 right one, and 1 iiad come to that conclusion before making 

 myself acquainted with the paragraph quoted ab;)V.^., wiiile 

 getting together the literature of the subject. All the facts 

 that 1 have been able to bring forwai'd in this paper tend, as 

 it appears to me, to show that we have here a unique case 

 among the Oligochfeta of encystment. I believe I am right 

 in saying that no freshwater Annelid has hitherto been dis- 

 covered to possess this power of temporary encystment. I 

 shall now endeavour to show that y3^olosoma does encyst 

 itself. 



On the hypothesis that the cysts in question are cocoons 

 we have to dispose of a good many preliminary difficulties. 

 In the^rs^ place their form — absolutely spherical and without 

 processes at either end — is unique among the Oligochteta ; 

 ^olosoma of course may be an exception, but there is not, I 

 think, evidence at present that it is. Second^//, there is the 

 difference of size ; no doubt there are infinite variations in the 

 size of the cocoons of various species of Oligochata, but I 

 have not found such a great difference as I have recorded here 

 among the cysts of yEolosoma. This very fact seems to indicate 

 that ilaggi's figures, to which I have already referred, repre- 

 sent cysts (of various sizes) and not developing ova ; the 

 figures of the contained embryos which he gives are not suffi- 

 ciently detailed to enable one to be absolutely certain that 

 they are not disintegrating worms rather than developing 

 embryos. The difference in shape between the structures 

 figured by Maggi and those which I have observed may be 

 possibly put down to specific differences. Thirdli/, all the 

 cysts which I examined — amounting to forty or fifty — ■ 

 contained fully grown worms, immature certainly (as regards 

 absence of sexual organs), but quite as large as those 

 swimming about in the same w ater. This may be merely a 

 coincidence, but in that case it will be a very remarkable one ; 

 all that we know of the development of the (Jligochteta shows 

 that the time varies somewhat in individuals, one growing 

 faster than another. Besides this we have further to assume 



Ann. d- Maff. X. Hist. Ser. 6. Vol. ix. 2 



