STUDIES OX THE ECTOPAEASITIC TEEMATODES OF JAPAX. 23 



piece, together with the basal piece, encloses the wall like a picture in 

 its frame. The muscular fibres are attached to the basal piece, and 

 are direct continuations of the longitudinal fibres of the body. In 

 0. 7najor the marginal chitinous piece is longer than in 0. minor. 



In Dididopliora (PI. X) the four pairs of suckers are, as already 

 stated, borne, in most species, each at the top of a pedifcel.; but in 

 Diclid. sessilis the stalk is very short, and in Diclicl. tetrodonis entirely 

 wanting. But that these species ai-e to be included in the same genus 

 will, I believe, be scarcely contested by any one who has studied their 

 anatomy. The suckers ai'e in a, surface view usually circular, as in 

 Diclid, sessilis and Diclid. elmgata, but are sometimes slightly elliptical 

 as in. Diclid. tetrodonis, and are arranged in a semicircle or horse-shoe 

 shape. Each sucker is as a whole nearly hemispherical, and its open 

 end is directed obliquely towards; the ventral side. The wall consists 

 of prismatic fibres, and is divided into four equal parts by as many 

 chitinous rods radiating from the centre of the sucker (PI. XII, fig. 

 4). The whole number of the chitinous pieces is eight for each.sucker, 

 and are represented in their natural positions as seen from, the surface 

 in fig. 1, PI. XII. A T-shaped piece (a) is situated with the point of 

 junction of the leg and arms exactly in the centre, with the two 

 arms of unequal length extending some way towards the periphery of 

 the sucker, and, the leg extending quite to the periphery and here 

 dividing into two branches which diverge from each other in a diame- 

 trically opposite direction. The portion of this chitinous piece corres- 

 ponding to the leg of the T is hollow, but the remaining portions are 

 all entirely solid. Another hollow piece (b) extends from the centre 

 in an opposite direction from the leg of the T-shaped piece 

 towards the periphery, which it, however, does not reach. The hook- 

 like piece marked c is paired, and bears at its angle a process which is 

 seen in sections to lie outside the substance of the fibrous wall (PI. 



