58 



LECTURE V. 



28 



appendage is spirallj'^ disposed when flaccid, is tubular, and distinctly 

 perforated at the apex. 



The ovaria occupy the whole margin of the body for a line in 

 breadth : they consist of minute, branched tubes, in which the ova 

 are developed, as in acini. The oviducts are close to the ventral 

 integument, and terminate in a single large uterine canal, which is 

 disposed in many convolutions between the subventral acetabulum and 

 the bursa penis : it terminates by a vulva, or distinct pore, innnedi- 

 ately behind the male bursa. The ovarian ova ai'e colourless and 

 pellucid, but become opaque as they approach the oviduct : having 

 entered this tube they acquire a white glistening tunic, and after- 

 wards a yellow colour, which becomes deeper as they approach the 

 vulva. 



The Distoma lanceolatum {Jig- 28.) has been regarded as the young 

 of the Distoma hepaticum ; but it is of a different form, 

 has a different anatomical structure, particularly as re- 

 gards the alimentary canal, and its title to rank as a 

 distinct species is sufficiently vindicated by its power 

 of developing fertile ova without changing its cha- 

 racteristic shape or increasing in size. It rarely equals 

 five lines in length, but is more commonly three lines 

 long ; flat, lanceolate, more attenuated anteriorly, and 

 with an obtuse caudal apex. 



The suctorial pores are relatively larger than in the 

 D. hepaticum. The anterior globose sucker (a) looks 

 downwards, and is perforated in the centre by the 

 mouth: the genital pores are half way between this 

 and the hinder sucker (6). The transparency of the 

 integument allows the internal parts to be readily 

 discerned. The alimentary canal, commencing by a 

 kind of pharynx, is continued as a very slender tube (c) 

 to the bursa penis, where it bifurcates, each division 

 (rZ) being continued without farther ramification along 

 the right and left sides of the body to the tail, where 

 it ends in a blind extremity. The minuter excretory 

 svstem of vessels has not been discerned in this small Distoma. The 

 simplicity of its digestive apparatus makes the analogy very close 

 between the D. lanceolatum and the TcenioB. 



In the interspace of the two digestive tubes four opake whitish 

 spots are visible, of which the tliree anterior or larger ones (e) form the 

 testes. Each transmits from its anterior margin a very minute duct, 

 which, advancing forwards, unite in a common vas deferens, ter- 

 minating in a small vesicle at the base of the penis, which is pro- 



Dist. lanceolatum, 

 magnified. 



