496 JOSEPH STAFFORD, 



also generally narrows from the rim backwards and then about the 

 pharynx begins again to expand into the neck and body. The neck 

 may be so extended that the pharynx is far in front of the body. As 

 already noticed the form of the whole sucker may vary to a wonderful 

 extent, A particular, contracted condition is produced when through 

 muscular action, thickened upper and lower lips are formed, the side 

 walls remaining thin. 



The body-parenchyma passes continuously into that of the neck 

 and to the edge of the sucker without any sudden change of structure 

 but a gradual condensation of tissues. Probably the most noticeable 

 feature in sagittal or horizontal sections is the gradual thickening of 

 the deeply staining chromatophil layer in passing from body to neck 

 until anterior to the pharynx is completely filled with this tissue. 



The musculature shows here, in the dorsal region especially, the 

 stratum of longitudinal fibres well developed, reaching from near the 

 end of the upper lip back along the neck. Outside from these the 

 not very strong circular fibres which farther back in the neck reach 

 their greatest thickness. Below, at the outer angles of the mouth and 

 neck strong longitudinal muscles. Inside of these the diagonal muscles 

 which are probably better named inner circular, numerous across the 

 outer lower corners. Characteristic for the mouth sucker are the 

 radial muscles running from the inner cuticle, clothing the mouth 

 cavity, in straight lines to the cuticle of the outer surface. They are 

 best studied in longitudinal sections, or in cross sections if the state 

 of contraction permitted the sections to fall lengthwise along the 

 muscles. They are present as far back as to where the funnel con- 

 tracts into a small tube and appear then to be continued in less 

 numerous and more delicate strands that are not so regular in ther 

 direction. 



On the inner side of the mouth funnel are reflected the muscles 

 of the outer surface but they are not so strongly developed. Besides 

 these there are also muscles in special relations to different organs 

 but always in limited numbers of fibres. Where an upper lip thick- 

 ening is formed can also be seen transverse fibres or even fibres 

 crossing one another at an acute angle in the centre of the thickened 

 l)art and attached at both ends to opposite parts of the mouth cuticle. 

 These are probably part of the inner circular muscles. Then there 

 are fibres from the mouth to the pharynx, from the sides of the pre- 

 l)harynx diagonally to the middle of the ventral surface of the neck, 

 and also from the mouth cuticle to the outer corners of the lower lip. 



