KUMINANTIA 325 



with the fodder, or drink, to the digestive organs of the host. 

 In the case of Fasc. hepatica, as probably obtains also with 

 many other flukes, I think there can be no doubt that the Cercarige 

 pass directly into the bodies of ruminating animals. The cir- 

 cumstance that flukes of this species have been found beneath 

 the human skin shows how considerable are the boring powers 

 of the armed Cercarise. 



In regard to the possibilities of fluke development, that will 

 be best understood by glancing at the constitution of the zoolo- 

 gical individual. The sum total of the products of a single 

 germ may be tabulated as follows : 



Zoological individual (Fasciola hepatica). 



a. Ovum in all stages. "1 ,,. , ee .. , 

 ,..,..*. -u f First "biotome." 



b. Ciliated free-swimming embryo, J 



c. Nurse, germ-sac, sporocyst (redia),} Second "biotoine." 



d. Active, migrating, tailed larva (cercaria) ,~\ ^i 



e. Encysted, resting larva (pupa), > (( biot ^ me 



f. Sexually-mature fluke (fasciola). J 



This is a fair representation of the life-phases of the fluke. 

 The life-phases are rarely less numerous or complicated than 

 here indicated, but Pagenstecher's researches tend to prove that 

 under certain climatal conditions the number of larval forms 

 may vary considerably. In other words, the fluke individual 

 does not comprise any definite number of " zooids," although 

 the kinds of zooids are limited. I recognise three (C biotomes." 

 The first includes ,only one temporary, independent life-phase, 

 this is the ciliated animalcule, which I call a " protozooid." 

 The second "biotome" may comprise only a solitary simple 

 sporocyst or germ- sac (deuterozooid), but an almost indefinite 

 multiplication of new and independent germ-sacs, as well as 

 other more highly organised "nurse formations," may also be 

 developed from the primary sporocyst (secondary and tertiary 

 "deuterozooid"). The third " biotome " embraces a large but 

 variable number of " tritozooids " (cercaria), an equal number, 

 whatever that may be, of " tetartozooids " (pupae), and, there- 

 fore, also, a similar number of " pemptozooids " (flukes). 



Practically, other curious results arise out of the foregoing con- 

 siderations. For example, a single sheep may harbor 1000 flukes. 

 Each fluke will develop 10,000 to 40,000 eggs. Each egg 

 may give rise to 370 zooids. It thus appears that, if all the 

 conditions were favorable, a single fluke might originate between 



