PLATVHELMINTHES 107 
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 hned by a layer of amoeboid 
cells, and the digestion of the solid 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 
o 
3. Genital pore. D. A ciliated internal end from the ex- 
4. Evaginated cirrus sac (? penis). cretory apparatus. 
5 ral aA . Is 
a nae 2 ee 1. Orifice of the flame cell (highly 
6. Vasa deferentia. ae ; 
= same aie magnified). 
7. Vesicula seminalis. 
8. Ductus ejaculatorius. E. Egg of Fasciola hepatica, x 330 (from 
9. Accessory gland (from Sommer). Thomas). 
