JENNINGS: DEVELOPMENT OF ASPLANCHNA HEKRICKII. 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. Eycles- 

 hymer ('95) experimented as to the effects of pressure ou the eggs of 

 Amblystoma tigrinum, and found that when the eggs were compressed 

 laterally to one half iheir 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." (Eycleshyiner, '95, p. 353.) 

 In experiments of a different natui-e, Morgan ('95) observed that the 

 shaken eggs of Sphferechinus 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 zoological 

 lines have not paid attention to the exact relations of the spindle to the 

 cell axes, so that' little was to be found in tlie 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 w'ith the 

 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 botanical literature the case was somewhat different, and seven 

 years before Hertwig ('93) 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 prismatische oder cylindrische Zellen der Lange 

 nach, wenn das Prinzip [of least surfaces] eine Querwand, der Quere 

 nach, wenn es eine Liingswand verlangte. So theilen sich oft die INIark- 

 zellen, die Zellen der Grundparenchyms sich entwickelnder Blatter 

 nur quer, ohwohl ihre Hohe im Vergleich zur Breite nur gering ist " 

 [Italics mine]. He had also given many examples of the conditions 

 thus characterized. 



Recently the attention of zoologists has been directed to a careful 



VOL. XXX. — NO. 1. 5 



