SEA-FISHERIES LABORATORY. 95 



there do not appear to be so many loculi in the bothridia 

 figured. 



The myzorhynchus is figured separately in fig. 10 A. 



It is very difficult to make out the structure of this 

 organ in whole preparations of the worm, but transverse 

 sections shew that it is essentially the same as the corre- 

 sponding structure in E. variabile. The terminal os leads 

 into a rather long canal which terminates in the opening of 

 a proboscidial sucker. The latter is represented by the 

 globular structure in fig. 10 A. It is, however, not 

 apparently muscular. The very prominent radial and 

 concentric muscle fibres represented in fig. 5 are quite 

 wanting, and in their place there is a rather loose connec- 

 tive tissue. The longitudinal retractor muscle bundles are, 

 however, represented ; they pass down in the external part 

 of the myzorhynchus and apparently originate in the walls 

 of the basal part of the latter. 



Echeneibothrium variabile, E. dubium and E. minimum 

 thus form a series characterised by the progressive 

 reduction of a functional myzorhynchus. In the first 

 species this organ is large and well developed, and the 

 eversible proboscis contained in it may apparently act as 

 an actual organ of adhesion. In E. dubium the myzorhyn- 

 chus is still present, though greatly reduced in size ; and 

 the contained proboscis is also greatly reduced, and 

 cannot, apparently, be everted. In E. minimum the 

 myzorhynchus has entirely disappeared, and it is this 

 difference that appears to me to justify the removal of 

 the species from the genus in which it was originally 

 included. 



Rhinebothrium minimum (van Beneden). 



Habitat : Raia clavata and R. maculata. 



The difficulties presented by the systematic characters 



