62 A FURTHER KNOWLEDGE OF THE CYSTIC CESTODES, 



not advanced so far in development as the cysts containing two. 

 In one of the spirit specimens examined, a cyst was found con- 

 taining three equally and fully developed Cysticerci (Fig. 7). 



Structure of the cyst wall. — The outer wall of the cyst is com- 

 posed of a fibrous layer (Fig. 8, /. I.) continuous with the muscular 

 layer of the wall of the intestine and doubtless formed from it l>y 

 the replacement of its muscular elements by fibrous tissue. It 

 contains scattered cells, blood vessels, and lymph spaces and is 

 covered externally by peritoneum. Internal to this fibrous outer 

 wall and lining the cavity of the cyst is a thin layer of slightly 

 staining homogeneous substance, with flattened nuclei on its inner 

 face (A. I.). As in the case of the cyst wall of the Cysticercus 

 from Hoplocephalus, I attribute to these two well-defined parts 

 of the wall a distinct origin. The outer wall is a product of the 

 tissues of the host, while the thin inner lining of the cyst cavity, 

 together with the cellular network in its interior {seq.), are the 

 direct derivatives of the six-hooked embryo, representing the 

 proscolex or blastogen of Villot. 



The cavity of the cyst is occupied by a branching network of 

 cells, the nucleated cells from which the anastomosing processes 

 arise being situated irregularly in the angles between the meshes. 

 Round the periphery of the cavity of the cyst the processes of 

 these branching cells become continuous with the inner lining of 

 the cyst wall, a fact which supports the view expressed above, 

 that the inner lining of the cyst is an integral part of the parasite 

 and not derived from the host. 



Structure of the Cysticerci — The Cysticerci lie embedded in this 

 network, and, as they occur naturally in the cyst, are small rounded 

 or oval bodies, about -75 mm. in diameter, and with the head 

 invaginated at the broader anterior end (Fig. 9). When the cyst 

 wall is ruptured and the Cysticerci allowed to escape in a drop of 

 water, the head is immediately evaginated and they begin to creep 

 about actively; the change of shape is so remarkable that ihe 

 movement might almost be described as amoeboid. 



