60 INVERTEBRATE ANIMALS. 
occur in which the individual consists partly of similar zodids 
which remain permanently connected with one another, and 
partly of dissimilar zodids which are detached to lead an inde- 
pendent life, all alike being the result of the development of a 
single ovum. 
Zo0id.—The term “zodid” is indifferently applied to all the 
more or less completely independent beings which are produced 
by budding, or by cleavage froma primitive organism. It does 
not matter, therefore, for the purposes of this definition, whether 
these beings remain permanently attached to the original organ- 
ism, or whether they are finally separated to enjoy an indepen- 
dent existence. 
flydrosoma.—The term Piedrosorit "is one which is very 
conveniently applied to the entire organism in any Hydrozodn, 
whether this be simple, or whether it be composite and made 
up of a number of connected zodids. 
Polypite.—That portion of any Hydrozodn which is concerned 
with the process of digestion, or, in other words, the “alimentary 
region, is termed the “ polypite”—the more generally current 
term of “polype” being now restricted in meaning to the same 
region in the higher Celenterata (Actinozoa). In such of the 
FHydrozoa as the fresh-water polype or Hydra, in which the 
hydrosoma is simple, the whole organism is termed a polypite ; 
but the term is more generally employed to indicate the nutri- 
tive zodids of any compound Aydrozoon. 
Cenosarc.— The term “coenosarc” (Gr. koinos, common; 
sarx, flesh) is employed to designate the common trunk or flesh 
by which the separate polypites of any compound Hydrozodn 
are united into a single organic whole. 
Distal and proximal—These are terms applied to different 
extremities of the hydrosoma. It is found that one extremity 
grows more quickly than the other, and to this free-growing 
end—at which the mouth is usually situated—the term “distal” 
is applied. To the more slowly-growing end of the hydrosoma 
the term “proximal” is applied. When the Hydrozodn is fixed 
to any solid object, it is by the proximal end that attachment 
is effected ; but in such forms as are permanently free this mode 
of distinction is inapplicable. The terms may be used either in 
reference to a single polypite in the compound Aydrozoa, or as 
regards the entire hydrosoma, whether this be simple or com- 
pound, 
