THE SCOLEX POLYMORPHUS 847 
mountable one. The ragged and irregularly constricted ends 
of some of the specimens (figs. 7 and 8) suggest that part 
of the body is being lost, as in the case in the development 
of the strobila in those forms which have a typical bladder-worm 
stage. Again, while the body region is smaller than that of 
the larger specimens of the S. polymorphus (fig. 12) the scolex 
of the young P. triloculatum (figs. 9, 10 and 11) is considerably 
larger than that of the S. polymorphus. I should also add that 
fig. 12 represents one of the very largest of the larvae and has 
been killed under pressure to flatten the body and make it more 
suitable for a whole mount whereas the specimens of P. trilocula- 
tum were killed without pressure and the body has remained 
cylindrical. The 8. polymorphus reaches this size (fig. 12) only 
in the cystic duct and the smaller specimens present a lesser 
disparity in size. I am inclined to think that in the case of such 
large specimens portions of the S. polymorphus body may be 
moulted off just as in the case of the bladder portion in the cys- 
ticercus. One constant feature of the larger specimens of the 
S. polymorphus has, perhaps, some significance in this connec- 
tion. It is the occurrence of a denser region which terminates 
abruptly a little way behind the scolex (fig. 12). In a specimen 
stained and mounted whole after the carbonate of lime gran- 
ules, which occupy so much of the parenchyma in the body 
region, have been dissolved out, one can distinguish this region 
as having the same denser appearance as the tissue in the body 
of the young Phoreiobothria (figs. 10 and 12) or the region of 
proglottid formation in young specimens of C. laciniatum. It 
is possible that the scolex and this region of the S. polymorphus 
are the most important in the formation of the adult worm and 
that part or the whole of the body region may be lost. It seems 
probable that larvae like the 8. polymorphus have been derived 
from larvae of the cysticercus type and, if this be the case, it 
would not be surprising to have a part of the body region lost 
at this point in the development. 
