60 ANIMAL PAEASITES. 



with the most various Tceniae which pass through a vesicular con- 

 dition, and which succeeded with all species, with the exception 

 of the Tanite of the Echinococci, where an unfavorable accident 

 may have prevailed, we sum up what we know of the development 

 of these species, the following appears to be the case. According 

 to Leuckart, at least in experiments with T. serrata, we find, 

 twenty-four hours after administration, the six-hooked embryos 

 in the blood of the large abdominal veins (especially the vena 

 port a), and, on the fourth day, in the livers of rabbits to which 

 they have been administered, .small, white, clear vesicles, of 

 0'3 millim. in diameter, but rapidly increasing in size, which, on 

 the sixth, are already 1 millim. in diameter, and can only be 

 isolated with difficulty. They consist of white masses of areolar 

 tissue, deposited in strata, with bacillar and fusiform nuclei, and 

 of the embryo, which is only Ol millim. in length, and O05 millim. 

 in breadth. On these masses we distinctly see the above-described 

 conversion into areolar tissue and serous cysts, and in them the 

 formation of fatty aggregations (probably from decomposed cells), 

 which subsequently become calcified. But these masses are by 

 no means secreted only on the spot where we finally meet with 

 the vesicular worm. The very distinct yellow streaks, or passages, 

 formed of soft, yellow, exudation-mass, which, during the first 

 fortnight after the administration of the Taenice, give the surface 

 of the infested organs (for example, the brain and liver), an 

 appearance as if microscopic field-mice or moles had been bur- 

 rowing through them, prove clearly that the brood, at all events 

 of many species, undertakes a further active migration in or upon 

 the organs in question, which of course cannot be effected without 

 irritation, inflammation, and functional disturbance, as has already 

 been remarked. I pass over the particular symptoms thus pro- 

 duced. Every one will know in what they consist, by remem- 

 bering that they coincide with those of an inflammatory irritation 

 of the organs in question. Lastly, at the end of such streaks or 

 passages, which become filled by injections from the principal 

 veins, in consequence of the occurrence of rupture, according to 

 Leuckart, the embryo makes its appearance in the form of a clear 

 vesicle. In T. serrata the actual embryo, after the lapse of 

 fourteen days, measures 1*5 millim. ; in Ccenurus it is about the 

 size of a grain of millet, at this period. The small vesicle (the 

 worm), after it has begun to grow clear, acquires, in its interior, 

 numerous large, clear, enucleate vesicles, which, according to 



