THE CYSTIC ENTOZOA. 479 



exit to its young (for it is by the dilatation caused by the 

 young within it that the parent sac gives way), it soon becomes 

 unable to extract proper nourishment from the infested being, 

 the young within it become decomposed, and the whole animal 

 degenerates either into a firm cicatrix, or, as is most general, 

 into a fatty cretaceous matter. I have in many instances 

 found this matter forming upon the external coats of young 

 secondary hydatids, which were confined, as above stated, in 

 old and degenerating parent sacs. In general this cretaceous 

 matter originates in the internal and germinal membrane of 

 the parent sac ; these two membranes in old hydatids being 

 always thick, gelatinous, and homogeneous, like pure gelatine. 

 This thick gelatinous membrane presents no trace of the two 

 membranes of which it originally consisted ; it is generally 

 about the eighth of an inch in thickness, and lies in the most 

 dependent part of the cavity, quite loose and detached from 

 the external coat. It presents no trace of young vesicles or 

 hydatids, but has upon its internal surface a number of white, 

 opaque, fatty looking spots of all. sizes. Similar spots, but of 

 much smaller size, are also to be seen in the substance of the 

 membrane, and when examined by the microscope, present a 

 peculiar cellular network. As these spots become larger, they, 

 from being quite smooth, become rough and nodulated, each 

 of the cells being apparently filled with the peculiar fatty 

 substance. As this mass increases in size, it becomes more 

 cretaceous, and sends out branches in all directions, so as in 

 time to fill the whole cavity of the hydatid, which, as this 

 process is going on, shrinks up very much, so that it meets 

 the fatty matter, and enables the process of filling up to be 

 more speedily completed. Shortly before the cavity is com- 

 pletely filled up, the fatty matter begins to lessen in quantity, 

 being probably absorbed by the cretaceous matter gaining the 

 preponderance. In this way more or less of the whole mass 

 is absorbed, so that ultimately nothing is left but a small 



