JENNINGS: DEVELOPMENT OF ASPLANCHNA HERRICKIT. 65 
circumstances in deformed frogs’ eggs the first cleavage plane some- 
times, though rarely (Roux, ’94*, p. 274), passed through the greater 
axis of the cell, the spindle therefore lying in the shorter axis. Fycles- 
hymer (95) experimented as to the effects of pressure on the eggs of 
Amblystoma tigrinum, and found that when the eggs were compressed 
laterally to one half their normal equatorial diameter, there was little or 
no relation between the direction of cleavage planes and the greater or 
less dimensions of the egg. “The first vertical in the thirty-four eggs 
examined showed no constant relation to the compressed surfaces, in 
seven passing through the longest equatorial diameter ; in nine through 
the shortest ; in eighteen between the two.” (Eycleshymer, ’95, p. 353.) 
In experiments of a different nature, Morgan (795) observed that the 
shaken eggs of Spherechinus often divide at the first cleavage into 
three equal blastomeres, and in such cases at the next cleavage the 
three spindles lie in the short axes of the cells. 
When we turn to the evidence from observation of normal cell 
division, there is the same disagreement that is met with in the experi- 
mental evidence. Until within a few years investigators in zoölogical 
lines have not paid attention to the exact relations of the spindle to the 
cell axes, so that little was to be found in the literature to emphasize 
the necessity of caution in accepting at once the generalizations from 
the first experimental results. In cases where cells containing spindles 
were figured, there was generally an apparent agreement with tho 
principle that the spindles are in the long axis, but so long as it was not 
determined by observation whether this elongation of the cell was a 
consequence of the position of the spindle or a cause of it, the evidence 
was worthless, as pointed out by Heidenhain (94), and as clearly illus- 
trated in the preceding pages. 
In botanieal literature the ease was somewhat different, and seven 
years before Hertwig (793) had stated that the phenomena observed in 
cell division agreed “fast ausnahmslos” with his law, Berthold (86, 
p. 230), in his thorough and comprehensive work on the subject, had said : 
“Sehr oft theilen sich prismatisehe oder cylindrische Zellen der Länge 
nach, wenn das Prinzip [of least surfaces] eine Querwand, der Quere 
nach, wenn es eine Lüngswand verlangte. So theilen sich oft die Mark- 
zellen, die Zellen der Grundparenchyms sich entwickelnder Blätter 
nur quer, obwohl ihre Höhe im Vergleich zur Breite nur gering ist” 
[Italics mine]. He had also given many examples of the conditions 
thus characterized. 
Recently the attention of zoölogists has been directed to a careful 
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