454 The American Naturalist. [May, 
toplasm around the centrosome and also representing the astral radia- 
tions not as mere lines but as flat ribbons or plates. In the author's 
mind this means that the rays are not muscle-like fibrils, but the fused 
walls of alveoli or vesicles—hence their flat appearance. __ 
The main part of the paper is taken up with the consideration of cer- 
tain interesting experiments devised to illustrate the action of a set of 
contractile elements. Modifying the model of Heidenhain the author 
constructed a schema to illustrate cell division as follows: a circle of 
rubber tubing is made more or less rigid by steel rods inserted inside it 
or by means of a spiral spring—this represents the periphery of a cell ; 
from the periphery to the center are stretched elastic bands of rubber 
which represent the astral rays; these are attached to two masses 
(forming the hub in this wheel) which may be at the centre or separ- 
ated like the foci of an ellipse, when they represents the two centro- 
somes. According as the rim of the wheel is stiff or limp and the halves 
of the hub united or apart and according to the strength of the radiat- 
ing bands various forms will be assumed by the system when at rest. 
By this scheme the author makes clear that a system of radiating con- 
tractile elements in conjunction with a somewhat resistant periphery 
can make various diagrams that. show resemblances to phases of cell 
division in the behavior of the cell periphery, the length of the astral 
rays and the movements and positions of the centrosomes. 
Besides emphasizing the part played by the cell periphery the author, 
by ingenious contrivances, estimates the amount that this periphery 
must grow or enlarge during cell division and here again seeks to bring 
in the assumed nuclear loss of liquid as a factor in the new formation 
of cell surface. : 
Though in the main adopting much of the conception of Heidenhain 
as to the part played by a system of contractile elements, the author 
does not suppose these elements are persistent cell structures handed on 
from one cell to another to do the work of cell division. Moreover he 
does not regard such radiations, when they are present, as anything 
like muscle fibrils but merely as indications of a rapid extraction of . 
liquid leading to linear arrangements of vesicles and indicating lines of 
pulling force. 
Continuity of Cells in Eggs.—August Hammar of Upsala hav- 
ing previously found? that the cells of cleaving eggs of echinoderms arè 
connected by a superficial film of material, presumably protoplasm, has 
extended his observation and now claims that such intercellular con- 
5 See AMERICAN NATURALIST, July, 1896, p. 597. 
