66 BULLETIN: MUSEUM OF COMPARATIVE ZOÜLOGY. 
observation of these relations, and a number of facts are now at hand 
which bear upon the subject. 
Ziegler (95) has studied the cleavage of certain nematodes (Diplo- 
gaster longicauda, Rhabdites teres, and Rhabditis nigrovenosa) with 
especial reference to the relations of cell form to the direction of cleav- 
age, and finds that the conditions in these cases confirm throughout the 
law of Hertwig. In the normal cleavage the spindle always places 
itself in the long axis of the cell, even though a rotation of the nucleus 
and asters from their first position is often necessary to accomplish this 
result. And in cases where the egg is deformed by some outer agent, 
as pressure by the walls of the oviduct or the like, the normal position 
of the spindle is changed to agree with the changed form of the cells, 
the spindle lying in the long axis in every case. The agreement with 
Hertwig's law is complete. 
On the other hand, zur Strassen (95 and '96) has studied the cleav- 
age of another nematode, Ascaris megalocephala, with the same ques- 
tions in mind, and has come to opposite results. In tho two-cell stage 
one cell divides with the spindle in the long axis, the other with the 
spindle in the short, axis, and in later stages a similar independence of the 
position of the spindle and relative dimensions of the cell is shown. Zur 
Strassen (95, p. 86) concludes: “Ich halte vielmehr den Kern für be- 
fühigt, vermöge ihm inhaerenter Eigenschaften eine gewollte Theilungs- 
richtung herbeizuführen, selbst wenn mechanische Hindernisse von nicht 
unbedeutender Höhe dem entgegenstehen.” 
Other observations bearing upon this question are much scattered. 
Clases aro not uncommon in which authors have fignred spindles in the 
shorter axes of the cells, but unless the observer's attention has been 
especially directed to the question, such figures are of little value, since 
& slight change in the position from which the cell is viewed produces : 
foreshortening which gives very different apparent relative dimensions to 
the axes. Heidenhain (95, p. 553) gives a number of such cases, from 
most of which the evidence is weakened by this consideration. How- 
ever, the case mentioned by Heidenhain of the germinal disk of the 
cephalopod egg as figured by Watase (91) cannot be explained away 
upon this ground. 
Some other instances may be mentioned. 
In the formation of the “germ bands” in the Polychat Amphitrite, 
according to Mead (94, p. 467), “the axes of the spindles in these 
divisions lie in the shortest diameter of the cells, and apparently in the 
direction of greatest pressure.” 
