HEKATEROBRANOHUS SHRUBSOLII. 193 



Granting, therefore, that the cephalic tentacles of the 

 Spionidee are prostomial, there would seem to be little or no 

 doubt of their homology with the branchiae of the Serpulidse. 

 But may we grant this ? The transverse section of Nerine 

 given by Claparede in his ' Structure des Annelides seden- 

 taires,' 1873, pi. xv, fig. 1, would seem directly to contradict 

 Jacobins figure and explanation already referred to. Setse are 

 never found on the prostomium ; yet, according to Claparede, 

 there are setse at the base of the cephalic tentacles in Nerine 

 cirratulus.^ Also, according to Claparede (' Beobactungen u. 

 Anat. u. Entwickelungsgesch. wirbelldser Thiere,' 1863, 

 p. 71), and Claparede and Mecznikow {' Zeitsch. f. w. Zool.', 

 vol. xix, pp. 172 and 177), they develop not from the pro- 

 stomium but from the peristomium. Claparede evidently never 

 thought of these tentacles as being anything but peristomial, 

 and a good many of the figures in his 'Annelides Chsetopods 

 du Golf de Naples (1868) ' would seem to point to the fact. 

 He very seldom, however, gives here a ventral or lateral view, 

 and it is therefore very difficult to determine what is truly 

 prostomial. From dorsal views only one is very apt to mistake 

 the crest which is developed on the prostomium, but also some- 

 times on one or two of the segments as well, for the pro- 

 stomium. Whether Claparede would have come to different 

 conclusions had he had the question before him is of course 

 impossible for us to say, but he is, as a rule, such an accurate 

 observer that, without further examination of the same forms 

 that he describes, we are not, I think, justified in concluding, 

 as Meyer does, that this was a " Beobachtungsfehler." The 

 point can only be decided by a renewed study of the develop- 

 ment, and by further observations on the living in as many 

 genera as are obtainable,^ since in spirit specimens, even when 



degenerate from ancestors of now existing forms. Meyer's arguments are, 

 in my opinion, insufficient to prove this. 



' Unfortunately, in the only specimens of Nerine cirratulus I was able 

 to procure for examination the tentacles had fallen off, and I was unable to 

 confirm Claparcde's observation. 



2 The forms described in the ' United States Fishery Reports ' would no 

 doubt prove of great interest if properly figured, but unfortunately the writers 



