ENTOZOA. 81 



ated posteriorly ; from ten to sixteen lines in length, from four to 

 seven in width : the broad end sends forward a sort of conical neck 

 or head, convex above, flat below ; one of the suckers (a) is at 

 tlie extremity of this process, a little turned downwards, and is the 

 true mouth ; the other (6) is at the under part of the base of the 

 neck, is imperforate, and serves merely as an organ of adhesion. 

 Between these is a small depression (d) in which the genital pores 

 are placed : not unfrequently the curved or spiral penis may be 

 observed projecting from the anterior of these pores. 



The body is of a whitish yellow colour, variegated near the margins 

 by the yellow ova, and on the dorsal aspect by the brown colour 

 of the double ramified alimentary tube. The integument is soft : 

 traces of muscular fibres can hardly be discerned, except around the 

 larger subventral sucker. 



Dr. Mehlis*, who has given the best anatomical account of the 

 human Trematoda, describes and figures the nervous system of the 

 Distoma hepaticum as a delicate cEsophageal filamentary ring, with a 

 slight ganglionic enlargement on each side, from which minute fibres 

 pass into the oral sphincter ; and two large filaments pass backwards, 

 one on each side, as far as the ventral sucker. 



I have tested this description by a dissection of the largest known 

 species of Distoma, the Dist. clavatum, whose anatomy I have de- 

 scribed in the Zoological Transactions. You "may distinctly perceive 

 in this preparation f the oesophageal nervous circle, the small cephalic 

 filaments, and the two widely separated nervous chords of the trunk. 

 In this specimen also, you will see the integument raised as a distinct 

 membrane from the outer transverse muscular fibres, and a portion 

 of these is reflected from the inner longitudinal stratum. Feeble 

 analogues of these parts of the muscular system are doubtless pre- 

 sent in the smaller Distoinata of the human subject. Pigment-specks, 

 called " eye-specks,^' are present in the Polystoma of the urinary 

 bladder of the toad and frog, as in the locomotive ciliated larva of 

 most Trematoda. In the Polystoma six long muscles diverge from 

 the hinder part of the body to have an expanded insertion into the 

 convex sides of the six suckers. 



The sole aperture of the alimentary system is that of the anterior 

 pore, which is surrounded by the fibres of the suctorial organ. 

 The alimentary canal in the Distoma hepaticum is continued from 

 this pore for a very short distance as a single tube, and then bifur- 

 cates ; the divisions (^Jig- 36. c, c) diverge to enclose the bursa penis 

 and the ventral sucker, again approximate, and afterwards run 



* LXVm. p. 22. fig. 13. t Prep. No. 1292 E. 



