DR. COBBOLD ON ANIMAL INDIVIDUALITY. 169 



furnished with a multitude of " heads," the latter being the so- 

 called echinoeocci or scolices developed in a rather more complete 

 form than obtains in the case of Goenurus cerehralis. In fact, the 

 so-called "heads" are almost separable "phases," being attached 

 to the maternal larva by slender pedicles only. They are, indeed, 

 frequently found detached; but then it is questionable if they 

 have not already parted with their vitality. In this view I cannot 

 call them " zooids " ; bnt the daughter-hydatid formations, which 

 are developed within or without the original maternal hydatid, 

 are quite deserving of such distinction. The latter are separable, 

 organized life-phases, each of which, like its parent, may develop 

 a multitude of echinoeocci ; so that, under favourable conditions, 

 there is practically no limit to the number of " heads " which may 

 be generated by a proliferating hydatid ; consequ.ently, also, there 

 is practically no limit to the number of tapeworms liable to be 

 developed from the same source. The tapeworms in this case, 

 however, have only three joints capable of arriving at sexual 

 maturity, and only one of these is mature at one and the same 

 time. Whether or no these Tcenice are susceptible of indefinite 

 proglottis-multiplication, after the fashion of ordinary tapeworms, 

 is a point on which I am, at present, uninformed ; it is probable, 

 however, that the joints follow the ordinary law of successional 

 development. In either case our computation of the^^number of 

 zooids and eggs capable of arising from a single germ needs not be 

 affected by this consideration. Taking an average case of hydatid 

 development, and assuming the existence of conditions favourable 

 to the complete development of the entire progeny, a single germ 

 of Tcsnia ecMnococcus might, without any exaggeration, give us 

 between five and six million separate life-phases or " zooids," from 

 which, under like circumstances, there would result not less than 

 150,000,000,000 ova ! In this calculation I do not take into ac- 

 count the probability of any one tapeworm developing more than 

 three successive sexually mature segments, and I allow for each 

 proglottis (tetartozooid) 10,000 eggs. For each hydatid I allow 

 10,000 scolices, though one large acephalocyst may develop ten 

 times that number. As many as a thousand hydaljids, or more, 

 may be developed in a single "host"; but echinococcus-heads 

 are not usually present in more than a limited number of the 

 daughter vesicles. Were they less " cribbed, cabined, and con- 

 fined " than is usually the case, no doubt their power of developing 

 the so-called " heads " would be correspondingly increased. As 

 it is, we may truly say, " Quantitas sufficit.'" 



