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THE PRINCIPLES OF BIOLOGY. 
are readied by a circuitous route, the first stage is the 
formation of these small aggregates, which, under the name 
of cells, are currently regarded as morphological units.” 
Mr. Herbert Spencer then takes a comprehensive 
morphological survey of all the classes of the animal kingdom 
from the Protozoa up to the Vertebrata. 
In the Rhizopoda, the lowest division of the Protozoa, “ are 
presented, under various modifications, these minute portions 
of living organic matter so little differentiated, if not positively 
undifferentiated, that animal individuality can scarcely be 
claimed for them.” The well-known Amoeba is a type of this 
living matter or protoplasm in its simplest form. It is the 
“ clay ” from whence the “ bricks ” are to be evolved. 
Several examples follow, showing slight modifications. In 
Difflugia the pseudopodia are limited to one part only. In the 
Foraminifera, of which Gromia is an illustration, the sarcode 
is covered by a delicate calcareous shell, through the minute 
holes of which the pseudopodia protrude. The Infusoria are 
more highly developed, and “ in them we find along with 
greater definiteness a considerable heterogeneity.” The 
aggregate is an aggregate of the first order, but in these and 
in similar organisms “ the compound individuality is scarcely 
enough marked to subordinate the primitive individualities.” 
In a higher division, the Ccelenterata, the typical form of 
which is the Hydra , “ having specialized parts performing 
mutually-subservient functions; and thus exhibiting a total 
life distinct from the lives of the units.” The Hydra, there¬ 
fore, illustrates the aggregate of the second order and the 
“ massing of secondary aggregates into tertiary aggregates is 
variously carried on among the Ilydrozoa , the Actinozoa, and 
the Molluscoida .” Mr. Herbert Spencer, however, directs 
attention to the fact that in these divisions “ the component 
individualities are very little subordinated to the individuality 
of the mass they form—there is only physical unity and not 
physiological unity.” The united animals in nearly all the 
cases illustrated may fitly be compared to societies, the 
members of which co-operate to gain certain ends. It is 
pointed out that in some of the oceanic Hydrozoa —the 
Bhizostomes for instance—the integration is carried so far, 
“ that the individualities of the polypes are almost lost in 
that of the aggregate they form.” 
Before considering the next higher division — the 
Annulosa —several beautiful illustrations are given wherein 
“ successive individuals arising by continuous development 
are so budded-off as to form a linear series,” and it is 
remarked that “ survival of the fittest must tend continually 
