54. ANIMAL PARASITES. 



lets, if we except a single case by Leuckart ; but we may never- 

 theless regard this metamorphosis as proved, partly by experiment 

 and partly by analogy with the platycercal cestode-forms of this 

 stage of development in cold-blooded animals, as Stein and 

 Meissner have actually seen on the latter forms, the pretty large 

 booklets of the embryos of the mature Cestodea in question. 



The details of the processes of this metamorphosis are as 

 follows : the embryo, still furnished with its six booklets, begins 

 to swell by the reception of fluid (liquid nourishment), which is 

 secreted from the place in which it has established itself; this is 

 at first a fluid similar to protoplasm ; but after the formation of 

 the enveloping cyst, or after the cessation of inflammation, when 

 the creature lives free in the interior of serous cavities, it does 

 not agree so much in its composition with the serum of the 

 blood, as with the ordinary products of the secretion of serous 

 membranes (Luschka). 



" By carefully stripping off the inner surface of the cyst of a 

 Cysticercus tenuicollis from a he-goat," writes Luschka, " I 

 obtained objects, amongst which numerous roundish cells of an 

 average diameter of 0*016 mill, were remarkable. These con- 

 tained, in their interior, clear, roundish, larger or smaller por- 

 tions of fluid, which were partly separated by a fine molecular 

 mass (PI. I, fig. 10 a, b), and partly converted for the most 

 part into a clear mass of the same nature (fig. 10 c). In 

 certain of these cells I was able to convince myself of the escape 

 of hyaline drops from their walls, and of their coagulation on 

 the addition of acetic acid. For my own part I entertain no 

 doubt that these cells are of a secretory nature, and that by 

 their complete fusion, or by the escape of their contents through 

 the uninjured walls, the fluid which surrounds the worm within 

 its cyst is produced. I have recently found exactly similar 

 cells in the Graafian vesicles of man and various mammalia, 

 and attribute to them a similar connection with the formation of 

 the liquor folliculorum Graafii. In true epithelial laminae I have 

 only seen scattered roundish and polygonal cells, of which some 

 were without nuclei, whilst others possessed a distinct nucleus. 

 It is more than probable that these secretory cells are nothing 

 but metamorphosed epithelial formations." From this it appears 

 distinctly that Luschka has observed the same processes in this 

 case that he had previously noticed in the production of the 

 fluid of serous cavities, and we must accordingly suppose that 



