PLA TYHELMINTHES 1 07 



The cuticle which covers its body is inflected at the mouth, 

 and at the genital and excretory pores. The nature of the 

 cuticle, like that of Cestodes, is a matter of dispute, some 

 authorities looking upon it as a basement membrane, whilst 

 others hold the view that it is a metamorphosed layer of cells. 

 It is perforated by numerous fine pores, and is produced into 

 many backwardly-directed spines. 



The intestine, which consists of two main branches giving 

 off numerous secondary ones, is lined by a layer of amoeboid 

 cells, and the digestion of the sohd food, such as blood cor- 

 puscles, is intracellular. 



The reproductive organs are similar to those met with in 

 the Cestodes, with the addition of a channel known as the 

 Laurer-Stieda canal, whose function, although the subject of 

 much debate, still remains uncertain. The canal is given off 

 from the common duct of the yolk gland, just before it enters 

 the substance of the shell gland to unite with the oviduct. 

 The canal opens dorsally upon the surface of the animal. Two 

 views have been held as to its use : it is regarded by some 

 as the duct through which the spermatozoa enter the female 

 organs, and in Polystoma (Fig. 74, B) this has actually been 

 observed ; on the other hand it has been urged that in some 

 species, notably in Fasciola, it is too minute for this purpose, 

 and the second view has been propounded, that it acts as a 

 valve, and permits the escape of an excess of the secretion 

 of the yolk glands, or of spermatozoa. 



The method of fertilisation in the liver fluke is not very 

 definitely settled, probably self-impregnation takes place. 



The life -history of the Fasciola hepatica may be briefly 

 summarised as follows. The sexual form lives in the liver 

 and bile ducts of sheep and other domesticated animals. Its 

 fertilised eggs develop to some extent in the uterus, and 



3. Genital pore. D. A ciliated internal end from the ex- 



4. Evaginated cirrus sac (? penis). cretory apparatus. 



5. End of vagina. j_ Q^ig^^ ^j q^^ jj^^^g (,^11 (highly 



6. Vasa deferentia magnified). 



7. Vesicula semmalis. 



8. Ductus ejaculatorius. E. Egg of Fasciola hepatica, x 330 (from 



9. Accessory gland (from Sommer). . Thomas). 



