452 C. C. MACKLIN. 



vation of a binucleate cell in a young culture the good fortune 

 was encountered of witnessing this entire process in it. A graphic 

 register of the successive changes is afforded by the drawings 

 (Plate II.) which were made with the aid of a camera lucida at 

 the times stated. The following is extracted from the protocol 

 written at the time of examination : 



11.55 A.M. A typical connective tissue binucleate cell (Fig. 13) from a 1 9-hour 

 culture of 7-day chick heart was selected for observation. The two approximately 

 equal, sharply outlined nuclear sacs are in close contact, causing a flattening of the 

 apposed surfaces. Each nucleus contains a single, somewhat irregular nucleolus. 

 The cell is long and narrow, and the long axis of the nucleus is parallel with that of 

 the cell in which it is contained. A single centrosphere (c) is found opposite the 

 area of contact of the two nuclear parts. Numerous fat globules and mitochondria, 

 the latter showing characteristic movements, are seen. 



12.40 P.M. (Fig. 14). The nucleus is still double, and the principal change noted 

 is the appearance of an additional nucleolus in the lower nuclear part. 



i. 20 P.M. (Fig. 15). The two parts of the nucleus are distinct. Only one 

 nucleolus is now seen in each nuclear sac. 



1.50 P.M. (Fig. 16). The cell outline has become modified, the cell body being 

 shorter, and the long axis of the nucleus has changed so that it is now almost at 

 right angles to its former direction. The nuclear surfaces are in close contact and 

 the upper end of the membrane formed by their approximation is indefinite in 

 outline. 



3.05 P.M. (Fig. 17). The cell body has become more fusiform, and the long 

 axis of the nucleus has rotated through 90. The double membrane (formed by the 

 areas of nuclear wall in contact) dividing the nuclear portions cannot be made out 

 except at the left side, and there indistinctly. An indefinite, refractive substance, 

 granular in character, is scattered along the line where this membrane had been; 

 the nucleoli are indefinite, and the uppermost one has been joined by an additional, 

 very small, mass of the same character. The upper part of the nuclear membrane 

 is not so distinct as heretofore. 



It would appear that the change which has occurred in the part of the nuclear 

 membrane dividing the two nuclear sacs is a part of the general change affecting the 

 entire nuclear wall and leading to its gradual disappearance, and the process is 

 similar to that which occurs in the early stages of mitosis. 



5.05 P.M. (Fig. 18). The refractive material in the zone formerly separating 

 the two nuclear sacs is more prominent than before; it seems to be chromatin. The 

 nuclear membrane is faintly marked. 



Half an hour later this cell is seen to become gradually smaller, and to draw in 

 its processes. At the same time the nuclear parts become smaller. The nucleoli 

 also undergo diminution in size. Finally the cell takes a rounded and thickened 

 form 6.00 P.M. (Fig. 19) and is much more refractive than the cells surrounding 

 it: in fact it resembles a cell in the prophase of mitosis. The fat globules and 

 mitochondria assume a wreath-like appearance about the central clear space, in 

 which the nucleoli soon disappear. Though the main mass of the cell is almost 

 circular there are narrow processes attached to each pole. The cell remains ap- 

 parently unchanged for some time, though undoubtedly important readjustments 

 are going on within it. 



