VARIATIONS IN FORM AND SIZE OF THE BLADDER. 555 



the wall like the daughter-bladders of Echinococcus. According to 

 Heller, these bodies extend with the arachnoid, sometimes into the 

 third ventricle and into the lateral ventricles, and always retain the 

 same racemose appearance. 



We cannot doubt that mechanical forces, and especially pressure, 

 exert a determining influence on the shape of the bladder-worms. 

 This may be proved by the ellipsoidal shape of the muscular bladder- 

 worms, which gradually results, as we know, from the original 

 spherical form through the pressure exerted by the muscular fibres in 

 contracting. When such determining factors are absent, 1 and the 

 conditions of growth are the same on all sides, then the normal 

 spheroidal shape is retained. 



As the shape of the bladder is determined by the mechanical 

 factors of the environment, so is its size determined by the nutritive 

 conditions. The results of my experimental rearing of bladder- worms 

 proved that Cysticerd of equal age were not of equal size in different 

 parts of the body. Even in the same organ there are sometimes 

 larger and smaller bladder- worms side by side, and yet we cannot dis- 

 tinguish them either in age or in phase of development. The size is 

 on an average about that of a pea or small bean, but it is very vari- 

 able. The larger forms are generally found in the internal organs, 

 in situations especially where their growth is but little hindered, as 

 on the free surface of the viscera (liver and heart) and of the brain. 

 In the ventricles of the brain the Cysticercus cellulosce sometimes 

 grows to the size of a pigeon's egg. In the eye, on the other hand, 

 and especially in the chambers of the eye, the worm generally remains 

 small and stunted. 



After the death of the worm, a marked decrease in size at once 

 sets in. The bladder fluid is absorbed, the bladder itself collapses, 

 and the surrounding cyst, unless endowed with unusual power of 

 resistance, undergoes similar changes. In the muscles it assumes the 

 form of a long strip, hardly 2 mm. broad, lying between the fibres, 

 and has a tendinous appearance (Stich). Some traces of the former 

 parasites always persist, even though they be only the remains of the 

 capsule or its calcareous contents, by the action of acids upon which 

 a few hooks may sometimes be seen. 



It is not, however, always or exclusively the form and size of the 

 bladder which vary thus in different cases. The head not unfre- 

 quently exhibits great differences. This is especially the case in the 

 larger bladder-worms from the brain, of which I saw specimens whose 



1 Dressel once observed at the base of the brain an almond-shaped bladder-worm, 

 and rightly supposed that it owed its shape to the pressure exerted on it by the whole 

 mass of the brain. (Loc. cit., p. 17.) 



