FERTILE ANt) STERILE ECHINOCOCCI. 585 



animal form. 1 This report received strength from the fact that 

 some Echinococci have really but few or even no heads in their 

 bladders. This loses all importance, however, when one sees that in 

 the encysted Echinococci sterile bladders are sometimes found in the 

 same cyst with proliferating ones. The sterile bladders are, further, 

 not merely smaller, half abortive forms, so that they might be held as 

 immature, but on the contrary, they are not unfrequently the larger. 



I do not for a moment doubt that the imperfectly developed 

 Echinococci have often been regarded as acephalocysts. 2 From my 

 experimental observations I may consider it as settled that the heads 

 of the Echinococcus-bl&ddQis are formed much later than those of the 

 Cysticerci, at a time when the young worms have already grown to a 

 considerable size. Such immature Echinococci must therefore be 

 observed all the more frequently, since the development of these 

 animals takes an unusually long time. The Echinococcm-\)l&ddeTS 

 grow for fully four months and more before they are capable of pro- 

 liferation, and have then attained the size of a small walnut. This 

 is, of course, true only of those worms which develop from the six- 

 hooked embryos : for in the daughter-bladders, and in those budded 

 off on the outside of the mother-cyst, I have sometimes seen brood- 

 capsules of the size of a hazel-nut and less with heads inside them. 



The sterile Echinococci remain throughout life at an early stage 

 of development. They are like trees which never bear floweis or 

 fruit. In plants, sterility usually depends on the conditions under 

 which they live, and the same may be true of the Echinococci. In 

 point of fact, it has been repeatedly observed that in certain localities 

 the Echinococci are much oftener sterile than in others, the Echinococci 

 of the brain, e.g., more frequently than those of the liver, &c. 3 In 

 man this sterility is not unfrequently associated with the absence of 

 daughter-bladders, which is certainly a renewed caution not to em- 

 phasise too strongly the vegetative conditions in judging of specific 

 distinctions. Thus, in a case 'described by Charcot and Davaine 4 of 



1 See Tschudi, " Blasenwtirmer," p. 28. On the other hand, the animal nature of 

 these so-called "acephalocysts" is often distinctly denied, e.g., by Rudolphi, Blumenbach, 

 Heusinger, &c., and for a while by Kuchenmeister. But the latter was, as he himself 

 remarks ("Cestoden," p. 6, note), first convinced of his mistake by my demonstration of 

 the chitinous nature of the bladder- wall. And yet he sometimes gets the credit of being 

 the first to establish the true nature of the acephalocysts. 



2 Thus, e.g., by Kuhn, whose figures exactly correspond with the Echinococci, four 

 months old, of my rearing ("Rech. sur les ac^phalocysts, " Mem. Soc. hist. nat. Strassb., 

 t. i., 1830). 



3 On the whole, the importance of these results is but slight, as is evident from the 

 fact that the presence of heads and hooks is noted only in a very small minority of the 

 cases of human Echinococci. 



4 Mem. soc, UoL, p. 107, 1857. 



