The Histogenesis of Cysticercus pisiformis. 187 



parenchyma and are mthout a cuticula, at least the existence there- 

 of is not demonstrable at this time. They are more or less elongated 

 sacs containing a cavity the enlargement of which keeps pace with 

 their growth. 



These consist of a syncytium of loose parenchyma strands with 

 a few scattered nuclei. Such a larva is illustrated in Fig. 14. The 

 larva has been cut tangentially at one end, while the plane of 

 section is median at the other; thus at one end the wall of the 

 larva is seen in surface view, and in section at the other. The 

 interior of the sac contains a cavity traversed in all directions by 

 slender, very irregular, anastomosing strands of parenchyma, forming 

 a network in which are supported the few nuclei. These strands 

 are of a looser texture than in the fully developed larva and carry 

 scattered masses of protoplasm which vary considerably in size 

 giving the strands a coarsely granular appearance. The strands 

 themselves, independently of the adherent protoplasmic masses, vary 

 in size and are composed of the finest fibrillae visible under a 

 magnification of 2850 diameters. Here and there may be seen 

 darkly stained granules scattered thru the protoplasm which are 

 developing chromatin granules. A discussion of the origin of the 

 chromatin is given under Cytogenesis. Whether the fibrillae 

 represent the ultimate units of the parenchyma, and whether they 

 are in protoplasmic continuity thruout cannot be determined. It 

 seems probable, however, that this is so. That the fibrillae are 

 primitive and the protoplasmic masses derived is evidenced by the 

 fact that the bladder is originally composed of fibrillae, the granular 

 protoplasm appearing secondaril}'. 



The structure of the nuclei is essentially the same as that of 

 the cytoplasm, but discussion of them will be reserved for a later 

 part of this paper. It may be noted here, however, that they 

 present considerable variation in staining properties, size and number 

 of chromatin granules. 



Thus the cavity of the bladder is broken up into many irregular 

 spaces which communicate freely with one another between the 

 parenchyma strands. At this stage, therefore, excretion must take 

 place by direct osmosis between the cells and the bladder cavity; 

 if, indeed, some of the excreta are not passed outward into the 

 liver. A portion of the cavity is not traversed by parenchyma 

 strands. At no stage of development have I found a distinct mem- 



