94 
Transactions Texas Academy of Science. — 1906. 
person may lack certain qualities necessary either for its own exist- 
ence or for the propagation of the race. For individuals proeeding 
from the same parents are usually of different kinds, physiologically 
complemental to each other ; this is shown by the commonest form of 
dimorphism, the sexual. Or we find still more dependence of the per- 
sons in such a case as the bee : the drones cannot reproduce or build 
the comb, workers cannot fertilize eggs and under normal conditions 
cannot lay them, the queens must be fed by the workers and like the 
drones take no part in the architecture of the nest. In such an example 
no single person is a complete individual, capable of maintaining its 
own existence and of continuing the race ; but the sum total of them is 
a unit that accomplishes this. 
Or again there may be successional polymorphism : a. medusa pro- 
duces only polyps, and a polyp is necessary to engender a medusa; 
were either of these persons annihilated the race would end. There- 
fore wherever there is discontinuous development, metagenetic or 
heterogenetic, one generation is closely dependent upon the preceding 
so that we can say here is division of labor extended over more than 
one generation. One would derive an entirely erroneous idea of a 
metagenetic medusa were he to study only the medusa stage or only 
the polyp, he should understand both and their connection. 
In fact the only unit we can assume in our study to give the fullest 
expression to the polymorphism of individuals is the one which in- 
cludes the whole life cycle and all the kinds of persons of each genera- 
tion. This is the natural taxonomic unit of the lowest grade, an en- 
tirety and a microcosm in itself. It is the unit of the phylogenist as 
well as of the student of heredity, evolution and ethology. For it ia 
the one that gives the fullest expression to the phenomena of division 
of labor and reproduction. We may construct higher groupings out of 
it, or we may analyze it into its successive components: (1) gen- 
erations, (2) persons, (3) embryonic stages, (4) qualities, structures, 
substances and energies. 
Certainly the life cycle is a natural unit, and it may be found more 
comprehensive and fruitful than any hypothetical unit that has been 
conceived. 
