STRUCTURE AND DEVELOPMENT OF THE ECHINOCOCCUS-HEADS. 603 



If a coloured fluid be used, such as solution of carmine, the space 

 between the two bladders is immediately coloured, while the true 

 interior remains for a time clear. 



Structure and Development of the Echinococcus-Heads. 



Von Siebold, "Burdach's Physiologic," Bd. ii., p. 183, 1837. 



Huxley, "Anatomy and Development of Echinococcus veterinorum, " Proc. Zool. Soc., 

 xx., p. 110, 1852. 



Wagener, "Die Entwickelung der Cestoden," Nova Acta Acad. Cces. Leop.-Carol., 

 Bd. xxiv. Suppl., p. 34, 1854. 



Naunyn, "Entwickelung des Echinococcus," MuLler's Archiv f. Anat. u. Physiol., 

 p. 612, 1862. 



Rasmussen, "Bidrag til Kundskab om Echinococcernes Udvikling," Vid. Meddel. 

 not. Foren. Kjdbenliavn, p. 1, 1865. 



The Echinococcus remains for a certain time in the condition which 

 we have described, but after perhaps five months, and when it has 

 become a bladder of 15 to 20 mm., it attains its full development by 

 the formation of the heads, which bud forth in ever-increasing 

 numbers from the parenchyma. 



It is thus the presence of the head that characterises the adult 

 Echinococcus, and that not of a single one or of a few, but of many 

 thousands, all of which, so long as they live in their larval condition, 

 remain in connection with the bladder- wall from which they originate 

 and derive their nourishment. 



In structure and mode of development these heads exhibit such 

 numerous and important divergences from those of the other cystic 

 bladder-worms, that it is necessary to examine them somewhat more 

 closely. 



As has been already mentioned, the Echinococcus-'hQ^ in its adult 

 state consists of a solid mass of cylindrical form, in which, besides 

 the armed rostellum and the four suckers, there 

 is an egg-shaped posterior portion, which sometimes 

 passes by a broad base into the middle portion 

 bearing the suckers, or at other times is separated 

 from it by a constriction. The rounded end of this 

 posterior portion, in which we recognise the neck of 

 the future tape-worm, is furnished with a round 

 depression, destined for the reception of the muscular 

 stalk, by which the head is attached to its basis. 

 Even after the detachment of the stalk, the depres- 

 sion is, for a long time, distinctly visible. FlG 322. Head of 



The length of the head (in its extended state) is Echinococcus veteri- 

 at most 0-3 mm., and about the half of this belongs norum ' ( x 90>) 

 to the posterior portion, which is usually distinguished from the 



