JENNINGS: DEVELOPMENT OF ASPLANCHNA IHERRICKII. 67 
Wheeler (95, p. 309) states in regard to the first cleavage spindle of 
Myzostoma: “In Myzostoma the spindle does not conform to O. Hert- 
wig’s law, but always lies at right angles to the long axis of the often 
very narrow protoplasmie pillar of the egg." 
Castle (96, p. 250) states that in the division of the entoderm cells 
of Ciona the spindles in certain cases lie in the short axes of the cells, 
even when a shifting of the asters from a previous position in the long 
axis must have occurred to bring about this condition. Castle states 
that no mechanical explanation of this phenomenon offers itself, though 
he holds that “other things being equal, it is true that the spindle arises 
in the longest axis of the cell” (p. 231, note). 
Tn the decapod crustacean Virbius, according to Gorham (795), the 
egg is ellipsoidal in form, and the first cleavage spindle may occupy the 
long axis, or be more or less inclined to it, or may even be nearly at 
right angles to it. 
The cell divisions in the germ bands of Crustacea as described by 
Bergh (795), in which the spindles take the same direction for many 
cell generations, should be added here (sce also MeMurrich, 95); though 
tho evidence from these must be weakened in the eyes of the upholders 
of Hertwig’s law by the fact that before division the cells * wachsen nur 
in der Weise, das ihre Längsdurchmesser dem Querdurchmesser ziemlich 
gleich wird und dann tritt die Theilung ein.” 
The positive evidence upon the question from observations of normal 
coll division is thus rather scanty, though doubtless some additions 
might be made by a further study of the literature. 
From both experimental evidence and observation of normal division 
the only conclusion possible is, that in some organisms the spindle does 
take a position in the greatest axis of the protoplasmie mass, apparently 
without regard to other factors, while in other cases the position of the 
spindle is determined by other factors, without regard to the form of 
the cell. 
The result is at first thought not very satisfactory, but this is not the 
only organic phenomenon with regard to which such a conclusion must 
be drawn. A few examples will make this clear. 
Stahl (85) found that the direction of the first cleavage in the spores 
of Equisetum is determined by the direction of the infalling rays of light. 
A general statement of the effect of the direction of the light rays on cell 
division would take a form similar to the unsatisfactory conclusion above 
given for the shape of the cells. 
If we leave cleavage and take up other growth phenomena, such as 
