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HARPER: BINARY FISSION AND SURFACE TENSION 1 
The second difference lies in the very fundamental fact that, as 
noted, in Volvox the germ cell grows to relatively large size before 
dividing and the daughter cells grow in size between the successive 
cell divisions. This is a very long step toward the full metaphytic 
habit in ontogeny. It marks a return to the habit of the simple 
protophyte like the bacteria and the appearance of a new point of 
departure in the development of the morphogenesis of a metaphytic 
plant body out of the primitive habit of reproduction by swarm- 
spores which is seen in Chlamydomonas and Sphaerella. In these 
protophytes, the cell having reached maturity forms from four to 
eight swarmspores by rather rapidly succeeding divisions of the mother 
cell. They escape by breaking of the mother cell wall and then as 
free individuals proceed to grow to the size of the parent. 
Swarmspore formation in Chlamydomonas and Sphaerella is a step 
beyond the conditions in Euglena, for example, where in ordinary 
reproduction each cell division is followed at once by the individualiza- 
tion of the daughter cells and their independence as separate organisms. 
In these particulars we may distinguish three steps in the evolution 
of the metaphyte from the typical protophyte. 
r. Cell division, in simple, direct alternation with growth, reproduction 
and individualization, practically simultaneous and _ identical 
processes. Euglena. 
2. Cell divisions at unequal intervals, reproduction multiple and in 
alternation with growth. Individualization delayed. Chlamy- 
domonas, Sphaerella. 
3. Cell division and growth in direct alternation, reproduction multiple 
and individualization delayed by intercalation of a true em- 
bryonic period. Volvox. 
In Volvox individualization is already in essence the complex 
process of differentiation and maturing which we find in the highest 
plants and animals. In Gonium individualization of the daughter 
colony, as I have shown in a former paper (’12), is accompanied merely 
by certain gliding movements of the cells upon each other by which 
an approximation to a least surface configuration is achieved so far 
as is possible for sixteen ovoid cells arranged in a flat plate. 
In Volvox, with the retention of multiple or colony reproduction 
as in Sphaerella, we have growth intercalated again between each 
successive cell division and also a specialization in function between 
germ and somatic cells. Complete individualization is delayed till 
the colony has become very many-celled. What may be called a 
pseudo-growth comparable to the elongation of the cells just back of 
the root tip by absorption of water and the formation of large central 
vacuoles is also represented in Volvox by the formation from the cell 
