ANIMAL PARASITES. 55 



the fluid contents of the caudal vesicle of the cystic worms also 

 is not a direct ready formed transudation from the blood-vessels, 

 but that it corresponds with the normal secretion of serous 

 cavities. This also explains how the worm can thrive, living 

 freely in closed serous cavities of the body, as well as when 

 enclosed in cysts, which, as we have said, are to be regarded 

 as analogous to these serous cavities, and also why this fluid 

 should not be so rich in albumen as is commonly supposed. 

 I have convinced myself that the nature of the fluid scraped off 

 the inner surface of the enveloping cyst exactly corresponds with 

 that of the synovia furnished by the serous synovial membranes. 



Besides the larger clear bodies, of which Luschka speaks, I 

 also found a considerable number of small, clear, pellucid bodies, 

 which resemble the calcareous corpuscles of the Cestodea. Are 

 these structures a regular product of the serous membranes, 

 which, if we bear in mind the occurrence of calcareous con- 

 cretions in the articular cavities, must at all events be rich in 

 lime? 



In the Echinococci, in the fluid of which Heintz found succinic 

 acid, the process is not so readily intelligible, as in these a very 

 intimate and nearly organic connection takes place between the 

 worm and the cyst. In this case we must suppose either that 

 the inner wall of the enveloping cyst continues imperceptibly to 

 perform the functions of a serous membrane, or that the inner- 

 most layer of the Echinococcus itself takes the place and per- 

 forms the function of a serous membrane. It is true that the 

 structure of the walls of this cystic worm gives no support to this 

 view, to which, however, Eschricht's statements upon the struc- 

 ture of the innermost layer in Echinococcus scolicipariens may, 

 perhaps, have some relation. Perhaps the fact here referred to 

 may furnish us with a further explanation of the circumstance 

 that cystic worms do not occur so much in cold-blooded as in 

 warm-blooded animals, when we have acquired some more certain 

 knowledge of the functions of the serous membranes in these 

 two groups of animals. I must, therefore, request that in the 

 discussion of the question why cystic worms only occur in warm- 

 blooded animals, besides the reasons which I have endeavoured 

 to adduce in my little work, ' Uber die Cestoden im Allgemeinen 

 und die des Menschen im Besonderen, Zittau/ 1853, the fact 

 here mentioned may also be tested. In this way the swelling of 



