168 DR. COBBOLD ON ANIMAL INDIVIDUALITY. 



d. Sexually immature tapeworm 



e. Matui'e tapeworm-colony, or strobile >• Second " biotomeJ 



.... } 



f. Segment, free-joint, or 'proglottis } 



At first siglit, tMs representation appears to be the same as 

 that of the Tcenia serrata, already given. It is, in truth, zoologi- 

 cally equivalent, but the component life-phases are both struc- 

 turally and numerically different. The " resting larva " of Tainiaf 

 serrata consists of a single free s.coles, whilst the resting larva of 

 T. ccenurus comprises a multitude of conjoined, inseparable scolices. 

 In the one case the scolex is a true " zooid," in the other it is the 

 merest fraction of a "zooid." In the case of Tcenia serrata one 

 single egg, under the most favourable conditions, can only lead to 

 the development of one tapeworm j but, iinder like circumstances, 

 the single egg of T(Bnia ccenurus may lead to the formation of at 

 least 300 tapeworms. This is accomplished when the Ccenurus of 

 the sheep's brain is transferred to the stomach of the dog, and all 

 the scolex-heads with which it is furnished become developed into 

 tapeworms. If we call to our aid an estimate of the " zooids," 

 the result is much more markedly significant. On the plan of 

 interpretation previously adopted, the "zoological individual" of 

 Tcsnia serrata (allowing 500 proglottides for the strobile) would 

 only yield us 503 " zooids " (as I have defined them) ; but in the 

 case of Tcenia ccenurus this representation would certainly give us 

 as many as 1,500,000 " zooids." Then, as regards the total 

 number of eggs produced by aU the final " zooids " collectively, 

 we should, in the case of Tcenia serrata (allowing each proglottis 

 to contain 5000 ova), obtain the comparatively small total of 

 2,500,000 eggs ; whilst in the case of Tcenia ccenurus, the progeny 

 of a single germ would collectively give out no less than 

 7,500,000,000 ova ! Lastly, let us glance at the possible results de- 

 rivable from a consideration of the " zoological individual" of Tcenia 

 ecJiinococcus, which may be tabulated after the same fashion : — • 



ZooLO&iCAii iirDiviDU.41 {TcBtiia echinococcus). 



a. Ovum in all stages 1 



h. Six-hooked embryo, boring larva, or proseolex ... j- First " biotome." 



c. Resting, acephalooystic larva (hydatid) J 



d. Sexually immature tapeworm 1 



e. Mature tapeworm-colony, or strobile > Second " biotome." 



f. Segment, proglottis, or free-jomt J 



Here, again, the representation is as simple as obtained either 

 in the case of Tcsnia serrata or in Tcenia ccenurus ; but, in point 

 of numerical and structural detail, the life-phases are remarkably 

 diflerent. In this case the " resting larva/' as in Ccenurus, is 



