349 



is therefore changed and we have now to account for the missing sixth 

 pair of parapodia, it seems probable that the pair of penes are homo- 

 logues of parapodia and represent the vanished pair. This theory strikes 

 rae as a quite likely one and certainly less far-fetched than "Wheeler's; 

 1 do not however wish to insist on this point as such homologies, based 

 on mere supposition and not backed up by any phylogenetic or onto- 

 genetic evidence, cannot be of any real value. 



Consideration of the above-mentioned points leads one naturally 



Figure 2. Myxostoma niochianum \. Gvniï. (after von Graff). »S3 = third 

 sucker, labelled (5 in the original figure. 



to consider the question : — is it possible that some of the other de- 

 scribed species of Myxostoma bear more than four pairs of suckers? 

 These organs are often very difficult to make out on unmounted spe- 

 cimens, a fact which the majority of workers on this subject have com- 

 mented on from time to time; von Graff, for instance, in his report 



