JENNINGS: DEVELOPMENT OF ASPLANCHNA IIERRICKII. 59 
by Berthold’s principle, so that all the cases cited later as opposed to 
Hertwig’s law can be utilized equally well against the prineiple of least 
surfaces as a determining force. 
It should be noted that Derthold did not in any sense maintain that 
this principle is the decisive factor in cell division, or the arrangement of 
cells in tissues. He recognized that the conditions in a living cellular 
body are widely different from those in a simple vesiculated fluid, and 
that the conditions actually found in plant tissues are often inexplicable 
by the principle of least surfaces, — in many cases, indeed, directly 
opposed to it. “ Aber nothwendig ist das in der Zelle nicht, wie bei den 
Flüssigkeitslamellen. Denn wir sahen schon früher, dass die Symmetrie- 
verhältnisse der Zellen von der äusseren Form oft vollständig unab- 
hängig werden, und auch unter Mitwirkung der äusseren Formverhältnisse 
können bei dem ineinandergreifen der verschiedenen Factoren sich Thei- 
lungsrichtungen ergeben, die mit den Forderungen des Princips der 
kleinsten Flächen nicht in HAE ARI: stehen." (Berthold, '86, 
p.230.) Berthold ('86, p. 230, Taf. 4) describes and figures many cases 
in which the arrangement and division of cells is not in accordance with 
the principle of least surfaces, 
The fact that a single cell may at one time take such a form as that 
which 49? shows in the surface view in Figure 37 (Plate 5), and in 
section in ER 38, and at another time have the form exhibited by the 
same cell in Plate 7, Figure 54 (surface), and Plate 6, Figure 48 (section), 
while the shape of the egg remains unchanged, demonstrates that we are 
not here dealing with a problem of the staties of a vesiculated fluid ; 
a single simple principle can no more account for the forms taken than 
it can for the protean changes of shape of an Amoeba, 
By this I of course do not mean to imply that it is not possible, and 
perhaps probable, that the laws of surface tension do, within certain 
limits, modify the form and arrangement of cells, as maintained and 
discussed at length by Berthold. Wherever the arrangement demanded 
by the principle of least surfaces is not in conflict with other purposes of 
the organism, or, to put it upon a less teleological basis, where it is not 
in conflict with stronger influences than the force of surface tension, the 
cells probably accommodate themselves to the demands of that principle. 
The point of importance, however, is that this is not a decisive factor, 
but may at once be overcome when other influences in the organism 
antagonize it. 
Zimmerman (93) holds that the general arrangement of cells in 
accordance with the principle of least surfaces in plant tissues is not 
