DE. COBBOLD ON ANIMAL INKIVIDUALITT. 167 



I conceive tliat Dr. Pagenstecher's apparently well-established 

 proposition (that " only such Trematode larvae as are capable of 

 arriving at sexual maturity are furnished vy^ith special appen- 

 dages ") gives strength to my views regarding the recognizable 

 epochs in the fluke-individual's life, and points to the line of 

 origin, continuity, and definiteness of the third "biotome " which 

 I have recognized on totally independent grounds. There is about 

 the same relative amount of individualized being in the cater- 

 pillar, pupa, and imago states of the Insect as there is in the 

 cercaria, pupa, and fluke conditions of the Trematode ; but the 

 "epoch" of the one embraces the whole life of the "zoological 

 individual," whilst in the other it represents only a section or 

 " biotome " of the life-cycle. If the term " zooid " be not allow- 

 able for the separate metamorphosed life-phases, as well as for 

 true gemmae, some other distinctive nomenclature must be sub- 

 stituted. I would like to see it retained to designate the semi- 

 individualized, separable life-phase, without regard to its mode of 

 genesis. 



Practically, other curious results arise out of the foregoing 

 considerations. For example, a single sheep may harbour 1000 

 flukes. Each fluke carries, I believe, at least 10,000 eggs. Each 

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

 conditions were favourable, a single fluke might originate between 

 three and four millions of individualized life-forms ; whilst the 

 solitary sheep itself would, under the same circumstances, be the 

 means of producing at least 3,000,000,000 fluke-zooids ! Happily 

 no such result as this can possibly occur in nature, since a multi- 

 tude of " interfering agencies " places the " favourable conditions " 

 in a comparatively insignificant minority. However, the balance 

 of parasitic forms from all cattle-sources is sufficient to destroy 

 thousands of sheep annually, to say nothing of the wounds in- 

 flicted on millions of small mollusks, into whose bodies the 

 " zooids " penetrate. 



Reverting to the Cestodes, the results attainable from particular 

 species are, in some respects, still more striking. Let us sepa- 

 rately examine the " zoological individuals " of Tcenia cosnwus and 

 TcBuia eehinococcns. The life-phases of the former may be tabu- 

 lated as follows :— 



ZooiiOaiCAL iiTDiviDtrAi {TcBnia coswurus). 



a. Ovum in all stages "j 



b. Six-hooked embryo, boring larva, or jjroscoZea; ... >• First "biotome." 



c. Resting, poly cephalous larva {Cosnurus cerehralis) J 



13* 



