6 FRANCIS H. WELCH. 
immersion in weak acids (1 to 10), but rapidly in stronger 
solutions with effervescence (fig. 6, a); these are greatly in 
the majority. (2) Ovoidal masses somewhat larger, uniform 
in structure, sometimes colourless, sometimes pale brown 
(fig. 6, 0); some of these, like the former, disappear under 
acids with effervescence, others resist all acids, but are 
soluble in liquor potassee, corresponding in this respect to 
small fat-globules and granules universally present im the 
parenchyma, and also within the visceral boundary in the 
visceral substance. (3) Angular or somewhat triangular 
or prismatic crystals, often aggregated in masses from six to 
ten (fig. 6, c), disappearing under acids without effervescence ; 
these are in the minority, but apparently are more numerous 
in some segments than others. Hence the corpuscles may 
be ranged in two classes—earthy salts and organic, the former 
composed of carbonate of lime (majority) or phosphates 
(minority), the latter of fat. Considering the invariable 
presence of the earthy nodules and crystals in all stages of 
segment development and their arrangement, it is difficult to 
resist the inference that their use to the parasite is that of 
giving a firmness and stability to the body structures similar 
to the spicules, and like earthy accretions in some of the 
lower organisms ; and their arrangement as isolated particles 
instead of continuous strands, while producing the requisite 
firmness, yet allows of freedom of movement of the body 
constituents, a feature necessary to the well-being of the 
parasite, as evinced by the great amount and direction of the 
muscular layers so conspicuous in the anatomy of this portion 
of the zooid. 
Enclosed within the body framework of the segment are 
the contained viscera and water-vascular system. These are 
situated in a distinctly defined central compartment, separated 
from the soft parenchyma of the body by a thick uniform 
boundary wall of fibrous tissue, and occupying about 4 of 
the entire proglottis and => in. in thickness. As seen in a 
transverse section the outline of this visceral space corresponds 
to the body-contour, an elongated ovoid (fig. 1, 6.), and, as 
exemplified in a vertical section, its diametcr is uniform from 
above downwards, except where the segments join (fig. 3, 3). 
It is supported by the transverse muscular bands, by some 
of the more internal longitudinal muscular bands, by delicate 
fibrous threads, and by strong radiating fibrous strands which 
connect the edges with the lateral edges of the segment. 
Within each lateral edge is situated the longitudinal water- 
vascular canal (fig. 1, c; fig. 2, ¢); traversing it at the lower 
part of each segment is the transverse or connecting water- 
