LIFE-HISTORY OF BUCEPHALUS HAIMEANUS. 663 
bodies are seen in the tail during developmental stages 
(fig. 34). 
As already noted, the contractile sac of the water vascular 
system opens into the lumen of the middle piece, and this, in 
turn, into the lumen of the appendages. When the water 
vascular sac contracts, its contents are forced into the middle 
piece and its membranous wall distended; when this wall 
contracts, the contents are forced into the appendages, which, 
as a result, become rigid. 
When the appendages are broken off, as frequently happens 
in free-swimming stages, thongh never within the sporocysts, 
the bladder-like portion of the middle piece collapses, and 
the definite form of the more solid portion may be seen (figs. 
26, 27, and 28). 
This portion is extremely muscular, and may undergo a 
great variety of changes of form. Tach side of the middle 
piece receives muscles from its own and also from the 
opposite side of the body (fig. 30). 
In B. haimeanus the “ wiilste”’ or “ scheiben”’ described 
in B. polymorphus are not present. 
The appendages are covered with a thin homogeneous 
cuticle similar to that covering the body. The appearance 
of “lasso cells” described by McCrady is caused by the 
refractive bodies already mentioned which lie upon the 
inside of each tail. 
_ Sections show a lumen situated just beneath these tracts 
of spherical bodies (figs. 32 and 33), the space between the 
lumen and the muscle layers being filled with a nucleated 
parenchymatous tissue. Closely applied to the outer wall 
are six double longitudinal muscle bands. Outside of these is 
the layer of circular muscle fibrils. 
From the study of the section of a tail the great improba- 
bility of Pagenstecher’s idea that the tails become sporocysts 
is at once apparent. In the sporocyst there is nothing 
corresponding to the supporting spherules or to the double 
muscle bands. 
