iSqs-J 65 [Hyatt. 
secondary products characteristic of the structures of the body or 
the colon}', and beside all these the sum of the load is continually 
acted upon by gravity which increases directly as the mass, while 
the strengtli of the materials remains more or less constant. 
Multiplication b}- fission among Protozoa beginning with a single 
zoon, as has been shown by Maupas, may reach through many gen- 
erations, but finally they die out unless reinforced by conjugation 
with another brood. These broods or disunited colonies, according 
to Maupas's observations, live and die collectively like the more 
complex and closely united colonies of cells making up the individ- 
ual among Metazoa, and thus the growth and development of cells 
in the latter and the free adult agamic generations of the Protozoa 
are, so far as we know, precisely parallel and both are ontogenetic. 
Agamic reproduction by fission alone is in other words a process 
of limited power extending only through a certain number or cycle 
of generations of cells in all forms, and so far as known dependent 
for its perpetuation and renewal in all organisms upon some form 
of conjugation. Cellular division, although distinct from the 
fissiparous modes of reproduction occurring in the building up of 
colonies of zoons in more complex organisms, Hydrozoa, Actinozoa, 
and so on, has nevertheless a similar result in so far as it multi- 
plies the numbers and adds to the mass if the daugliter zoons 
remain connected or to the number of generations if these separate 
and become individualized. 
It is of course not intended to ignore the great differences that 
exist between the separate generations of any organic process of 
multiplication and those that remain attached and form colonies or 
masses but merely to show that they agree in certain respects. 
The restoration of h>st parts or organs dependent upon the 
multiplication of cells is so intimately related to all forms of hyper- 
trophy and to asexual budding that these, in so far as they increase 
the masses of tissue, are properlj^ considered as part of the phenom- 
ena of cellular development. 
Those forms of gemmation which give rise to distinct zoons^ are 
iThis word was used in my "Larval theory of the origin of cellular tissue," ]>. 40, as 
a parallel term with "phyton" among plants, meaning in the animal kingdom any form 
having- typical structure of its own group or the elements of those structures. This is 
accurate in application to the Metazoa, but in speaking of a protozoan as also a unicel- 
lular zoon I went too far. A metazoan is also a multicellularzoonor metazoon; a sponge 
PROCEEDINGS B, S. N. H. VOL. XXVI. 5 AUGUST, 1893. 
