606 STRUCTURE AND DEVELOPMENT OF THE ECHINOCOCCUS-HEADS. 



But if the worm were exposed to the influence of external agents, or the 

 parenchyma brought into contact with water, or any other diffusible 

 fluid, the appearance altered, inasmuch as the brood-capsules burst, 

 and the heads contained in them became free. The latter were either 

 detached at once, or remained for a time in connection with the 

 shrivelled and rolled-up wall of the capsule, and were united in 

 groups, which were attached to the parenchymal layer by the stalk 

 of the capsule, irresistibly reminding the observer of a colony of 

 Vorticellce. 



FIG. 325. Closed and ruptured brood-cappules, showing their connection with 

 the parenchymal layer, (x 40.) 



There can be no doubt that it is these phenomena of incipient or 

 advanced maceration that have given rise to the numerous errors 

 regarding the structure of the Echinococcus, and the mode of develop- 

 ment of its heads, especially as the observations of Naunyn and Ras- 

 mussen have yielded results similar to my own. 1 



Kegarding the genetic relations between the JZchinococcus-he&ds and 

 the brood-capsules, I must again differ from my predecessors. While 

 they assert that the heads originate on the inner surface, and that 

 they are from the first solid processes, I must, on the contrary, refer 

 their origin to the outer wall, and maintain that, exactly as in the 

 Cysticerci, the first rudiments of the heads are developed in the form 

 of hollow buds. 



The buds situated on the outer wall of the brood- capsules had 

 already been occasionally observed, but they were generally mis- 

 taken, and regarded as adult heads, and on this ground many investi- 

 gators (including Huxley) maintain that the outer surface of the 

 brood-capsules is as well suited for the formation of heads as the inner. 



The great susceptibility of the brood-capsules to the influence of 

 reagents is explained by the thinness of their membrane, which even 



1 I must not, however, omit to mention that Klebs (" Handbuch der pathol. Anat.," 

 Bd. ii., p. 586) has lately reported that in the human Eckinococcus he has several times 

 found isolated heads situated directly upon the parenchyma. Frerichs and Sommerbrodt 

 are also said to have observed similar cases, 



