72 H. J. Clark on Polarity and Polycephalism. 
mative,unit, a zodlogical individuum, as the highest expression 
of unity attainable by the vertebrate zoiin. 
e duality, nay the plurality of the subdivision of the ver- 
tebrate axis, as illustrated by the embryo fishes of Lereboullet, 
is recalled in the diffuseness of the many hydre of the den- 
dritic Campanularie, or disguises itself under the interminable 
heteromorphism of the Siphonophors; it is polymerous but 
imorphous in Salpa, or polymerous but monomorphous in the 
fresh water Polyzoa; temporarily a polymerous, monomorphic 
wndirnduum in the fissigemmating Hydra, it eventually resolves 
itself into disconnected pseudo-individua ; for a time polymer- 
ous but dimorphic in the annelidan Myrianida of Milne-Ed- 
organ 
sais =, 
