l88 THE ANIMAL PARASITES OF MAN 



cyst developing from the oncosphere, in some cases (Ccenurus} in large 

 numbers, in other cases (Echinococcus} only after the parent cyst has 

 developed several daughter cysts. Released from its cyst and placed in 

 suitable conditions, it goes on living, and increases at its posterior end by 

 proliferation. In these cases a double change of generations must be 

 accepted (ONCOSPH^RA mother cyst ; SCOLEX, one or several in number 



PROGLOTTIDES). 



The view that the tapeworm consists of a colony originating from dimor- 

 phous individuals, and that its development takes place through an alternation 

 of generations, has been recently assailed by several authors. The cause for 

 this disagreement was furnished partly by changes in the views concerning the 

 alternation of generations itself, partly by those cestodes which exhibit 

 no external segmentation, as Ligula, in which the genitalia only are 

 repeated again and again, and partly by the so-called one-jointed cestodes 

 (Amphilina, Caryophyll&us, Gyrocotyle, &c.), the genitalia of which only 

 appear once in each specimen. Without arguing the pros and cons of 

 the opposing views, we must nevertheless remark that even though the 

 single-jointed cestodes must be considered the most primitive tape-worms, 

 it does not follow that the proglottides are merely segments of the body. 

 The advancement o'f a " morphologically strictly limited subordinate stage 

 of individuality " in itself essentially concedes the individuality of the 

 proglottides. If, on the other hand, the appearance of numerous little 

 heads in Ccenurus and Echinococcus is regarded as a multiplicate, there 

 is no reason why the formation of only ONE head in Cysticercus should be 

 anything else ; the NUMBER of the offspring^ is of no importance. A 

 difficulty is certainly presented by such forms as Ligula, but one can in 

 these either take it for granted that the formation of the proglottis has not 

 yet set in or that it has already disappeared. In the former case a lower 

 development of the single individual must be present, a view that can hardly 

 be opposed, as in other creatures forming colonies we know that there may be 

 a reduction of one or numerous individuals until only the stage of one organ 

 is left. 



If we except the tapeworms with only one proglottis, the 

 Cestodaria, we can always distinguish in the cestodes in the narrowest 

 sense, one scolex and a large or small number of segments (pro- 

 glottides). The SCOLEX serves the entire tapeworm by fastening it to 

 the internal surface of the intestinal wall, and therefore carries at 

 its end various organs which assist in this function, and which 

 are as follows : (i) SUCTORIAL ORGANS, i.e., the four round suckers 

 (acetabula), which are placed cross-wise at the circumference of 

 the thickened end of the scolex ; further, the double or quadruple 

 groove-like suckers (bothridia) which are diversely shaped according 

 to the genera and families. 1 (2) CLINGING ORGANS (booklets) that 



1 They may remain simple, and are then not separated from the remaining 

 muscles of the scolex ; or they rise as roundish or elongated formations over 

 the scolex, hollow on their free surface, and are often divided into numerous 

 areas by muscular transverse ribs. They may also carry accessory suckers on 

 their surface. 



