450 THEOPHILUS S. PAINTER 



As the aster assumes its new position, with high power, one 

 sees little clear vesicles lying on the edge of the centrosphere 

 on the concave side. These are the chromosome vesicles which 

 slowly fuse to form one nucleus, as the movement of the pro- 

 toplasm, described below, sets in. 



Following directly on these changes in the aster and in the 

 chromosomes, we have a series of phenomena which involves 

 the protoplasm of the egg. This is first seen in the ectoplasm 

 (or ' Verbindungsmembran' of Herbst, '00), which, on the side 

 of the egg opposite the concave side of the aster, (fig. 1) begins 

 to swell or blister. While this layer remains thin and difficult 

 to see, except in dim light, on other parts of the egg, in the 

 region opposite the aster it increases in thickness and frequently 

 becomes granular and more or less opaque. 



After the membrane swells, the whole area of protoplasm, 

 which it covers, begins to undergo a series of changes of contour 

 during which little ridges and depressions appear. These 

 rapidly change into pseudopod-like processes (fig. 2. In this 

 drawing as in the rest of the figures on this plate, the ecto- 

 plasmic layer is not shown) and the whole surface of the egg 

 becomes involved in a series of slow protoplasmic movements. 

 The mobility of the protoplasm is extraordinary. Figures 2, 3, 

 4, 5, 11, 12, 14 show typical cases in various phases of the 

 movement. The egg becomes flattened as the movement pro- 

 gresses and the finger-like processes undergo rapid changes in 

 shape like the pseudopods of an amoeba, and these processes 

 may even be cut off entirely from the egg (figs. 4 and 5). In 

 this event, however, they continue to undergo changes in shape 

 for a short time. 



As the radiations of the aster diminish in intensity and dis- 

 appear, the protoplasmic movements begin to subside. The 

 finger-like processes are withdrawn; the little protoplasmic 

 balls again fuse with the egg, (figs. 12 and 14) and the whole 

 egg becomes rounded out, in most cases, before the next divi- 

 sion cycle is well advanced. The large excentric nucleus and 

 the swollen ectoplasmic layer are the only features which show 

 that the ' egg has passed through the monaster cycle. 



