164 ENTOZOA. 



OHAPTBE II. 



FASCIOLA HEPATIOA. 



Development of Fasciola hepatica — Eggs and ciliated embryos — Injurious effects of the 

 liver-fluke upon man and animals — Symptoms produced by the Rot — Pathological 

 appearances — Treatment — Summary. 



Without attempting to enter into such minute details as would 

 extend this work beyond the proper limits, I shall here briefly 

 indicate the extent of our knowledge regarding the developmental 

 process so far as it concerns the earlier stages of the species under 

 consideration ; omitting all hypothetical views concerning the later 

 stages, because it is highly probable that we shall soon be in pos- 

 session of most of the principal facts relating to the phenomena of 

 the intermediate and later stages of development, as they occur in 

 this trematode. 



Development. — Stated briefly, the formation of the ova takes 

 place in this manner. Yelk globules pass down the various vitel- 

 ligene ducts into the main lateral and transverse efferent canals, 

 until they arrive at the point of union between these passages. 

 ISTear this situation, in an enlargement of the duct specially set 

 apart for the purpose, and where it is joined by a short germigene 

 duct, the globules congregate and surround the individual germinal 

 vesicles coming from the ovary. At this spot, therefore, we have 

 the earliest stage of egg-formation prior to the act of impregnation, 

 which latter function is accomplished by the union of the fine thread- 

 like spermatozoa almost at the same locahty, but a httle lower down. 

 The free seminal elements themselves form extremely delicate 

 threads, of an irregularly spiral form, and measuring the ^7 of an 



