166 DR. COBBOLD ON ANIMAL INDIYIDUALITT. 



This is probably a fair representation of the ordinary fluke 

 individual (Fasciola hepatica), in which species the entire life- 

 phases have not as yet been thoroughly identified. It is quite 

 certain that the life-phases are never less numerous or compli- 

 cated than is here indicated ; whilst 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. In the present case I 

 recognize three "biotomes." The first includes only one tem- 

 porary, independent life-phase ; this is the ciliated animalcule, 

 which, in my view, possesses sufficient individualized life to entitle 

 it to be recognized as a "protozooid." The second " biotome " 

 may in some cases 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 

 organized "nurse-formations," may also be developed from the 

 primary sporocyst (secondary and tertiary "deuterozooids"). 

 This reminds us of the practically indefinite number of zooids 

 (proglottides) which the second "biotome " of the Cestode gives 

 rise to ; but here there is analogy, and not homology. The third 

 " biotome " embraces a large but variable number of " tritozooids " 

 (eer caries), an equal number (whatever that maybe) of "tetarto- 

 zooids" (^pupce), and therefore, also, a similar number of" pemp- 

 tozooids " (flukes) . 



"Whether the views here promulgated be accepted or not, I 

 have, I trust, made it sufficiently clear that the fluke-individual 

 may comprise, in its life-cycle, a great and varying number of 

 life-phases, each of which may or may not possess equivalent 

 (and, necessarily, very limited) zoological value. The variabiKty 

 of the character of these life-phases is shown by tlie sporocysts 

 (deuterozooids), which are not only unequal to one another in 

 bulk, but also in organization, the higher forms (redise) deve- 

 loping a rudimentary digestive apparatus. Apparently the redia 

 is not, in all cases, an essential feature of Trematode larval life. 

 Putting together the whole possible and independent hfe-phases, 

 and placing their numerical development vdthin the lowest limits, 

 our ordinary fluke-individual would, I reckon, comprise about 370 

 "zooid" formations, those of the second "biotome" being pro- 

 duced by the well-known process of internal gemmation, whilst 

 those of the third "biotome" are the result of a simple yet pro- 

 longed metamorphosis. 



