446 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 



briefly the observations of a number of other investigators in regard 

 to these phenomena and the cytoplasrnic activities which have been 

 seen to take place in the eggs of a number of animals widely separated 

 morphologically. No definite conclusions are reached as to the 

 functions of these various phenomena, but it is generally thought that 

 they are concerned with fundamental intrinsic changes within the 

 cytoplasm. 



These protoplasmic connections are usually composed of the ectosarc 

 only. They are present not only in the two-celled stage, but in several 

 of the following stages as well. As the number of cells increases, the 

 connecting films become less easily recognized. 



The second cleavage occurs about twenty-five or thirty minutes 

 after the first. The plane of division is also meridional and at right 

 angles to the first segmentation. It begins at the center of the egg 

 next to the furrow of the first cleavage and slowly extends out toward 

 the periphery. When the division is completed the four blastonieres 

 undergo a slight rotation from right to left; and in the center of the 

 egg between the cells there is at times to be seen a small open space or 

 segmentation cavity which may extend through the entire egg as shown 

 in figure 21, plate 32. 



After a lapse of time equal to that which occurs between the first 

 and second divisions, the third cleavage furrow appears. This plane 

 of division is equatorial and divides the egg into eight blastomeres. 

 When the segmentation is first completed the two quartets of cells are 

 situated one upon the other and form a more or less spherical whole, 

 as is the usual arrangement in eggs in which segmentation is equal 

 and regular. This arrangement of the blastomeres is, however, of 

 very short duration, for soon a separation takes place between the cells 

 of the lower quartet and two of them roll away from the plane of 

 separation in one direction; the other two move out in the opposite 

 direction. In this migration the blastomeres move through an angle 

 of 45 degrees or more, and finally come to lie in such a position as to 

 form a semicircular plate as shown in figures 22 and 23 of plate 32. 

 The separation and rotation of the cells of one quartet seem to be 

 constant in their occurrence; but the final arrangement of the blasto- 

 meres is not always as regular and definite as that shown in the figure. 

 At times they are more loosely and irregularly connected, and may 

 assume relative positions similar to that shown by Aletschnikoff for 

 Oceania armata in figure 34, plate 1, of his "Embryologische studien." 



