ANIMAL PARASITES. 61 



Leuckart, are similar to sarcode drops. In the parenchyma we 

 recognise a cortical layer, which gradually becomes thinner, and 

 the cells of which are converted into muscular envelopes by 

 fibre-formation ; and a medullary layer, in which elastic vesicles 

 or cells occur in great quantity. From the appearance of the 

 medullary substance the growth of the little worm, which is 

 capable of motion even before the muscular layer makes its ap- 

 pearance, advances with particular rapidity. Even in the first 

 fortnight, and shortly afterwards, the form of the young cestoid 

 worm varies according to the species. Some, such as the youngest 

 Ccenuri, and Cystic, celluloses, tenuicollis, and fasciolaris, are 

 spherical ; others, such as Cystic, pisiformis, and probably also 

 Cystic, longicollis and fistularis, are more oval. Many of those 

 which are seated upon the surface of organs that project into 

 closed, serous cavities, continue to wander for a time in the organ, 

 until they finally fall into these cavities ; the oval forms appear 

 to have a greater desire for wandering than the round ones, 

 although this circumstance varies in itself, according to the dif- 

 ferent species, as we also observe such a wandering in the round 

 brood of Ccenurus. Up to the period above mentioned (about 

 fourteen days after administration), the changes here described 

 take place pretty universally, and in all places. But now, in all 

 those individuals which have reached situations in which they do 

 not find a favorable soil for their further development, there com- 

 mences a retrograde metamorphosis to the state of caseous, gra- 

 nular, tubercular, or atheromatose masses, in which we may 

 generally seek in vain for any remains of the embryo, although 

 this is certainly present. Many cases of miliary tubercular 

 disease of particular organs may indeed consist in nothing else 

 than the dead, fatty, and calcified young of worms. 1 As regards 

 the mode of disappearance of the above-mentioned passages, we 



1 As regards Cysticercus pisiformis, Leuckart places the escape of the Cysticerci into 

 the abdominal cavity in the third and fourth week ; and in this case the worm and the 

 enveloping mass are said to fall together into the cavity. But when this passage only 

 takes place about the fifth or sixth week, the worm escapes into the cavity of the 

 abdomen without its enveloping mass. All observations agree in showing that after the 

 expiration of eight weeks the second encystation in the abdominal cavity has taken 

 place ; and then the Cysticerci seated in the pelvic cavity and in the rectum, are sup- 

 posed to have escaped as Cysticerci from the liver into the abdominal cavity and passed 

 further on ; whilst I still believe that at least a part of them migrate there directly in 

 the form of young six-hooked embryos. 



