132 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, NO. 7 
In those coelenterates with division of labour the polyps are of three 
sorts, (a) nutritive, or sac-like, (b) reproductive, and (c) excretory, 
or ‘‘defensive.’’ If in strobilization of the fluke type buds of each 
of these sorts were formed internally, this would furnish the elements 
necessary for the creation of the so-called coelome, which is divided 
into three parts, (a) the perivisceral, or sac-like, (b) the gonadial, 
and (c) the excretory or nephridial. | 
The flukes and their allies always retain distinct traces of radial 
symmetry, especially in their digestive system and in the arrangement 
of their nerves. 
3. The turbellarians and nematodes are bilateral solitary animals, 
the individuals each comparable to a single coelenterate polyp. All 
of them show distinct traces of radial symmetry in their nervous sys- 
tem, and the turbellarians also in their digestive system. 
4. Such turbellarians as Microstomum are single animals each 
comparable to a single coelenterate polyp; but they divide in such a way 
as to produce chains of similar attached animals each of which is 
independent of the others and not a part of a more or less unified entity 
as in the case of the proglottides of the tape worms. 
The cestodes, the flukes, the turbellarians and Microstomum are 
all flat worms and all more or less closely related to each other. They 
all retain to a very considerable degree traces of radial symmetry and 
of other coelenterate features. Being intermediate between radially 
symmetrical and bilaterally symmetrical types it requires very little 
imagination to assume that they represent the four original types into 
which the coelenterates disintegrated upon the appearance of that 
developmental defect which resulted in bilateral symmetry. 
If the preceding suppositions are logical it is evident that the so- 
called evolution of the bilateral animals cannot be evolution in the 
sense of the progressive development of higher types from lower, but 
instead must have been a recombination and reassortment of the four 
diverse features characteristic of the four types into which the radially 
symmetrical colonial coelenterate type disintegrated. In other words 
the so-called evolution of animals is in reality a convergence toward a 
common centre from four equidistant points, and the progressive 
economic efficiency does not indicate any real phylogenetic progress, 
but results merely from a more and more intimate intermingling of, 
and a progressively better balance between, the main features indi- 
cated by the tape worms, flukes, turbellarians and Microstomum 
standing at the four corners of the original square. 
