34 
161. A series of PHOTOGRAPHS (each enlarged 1000 diameters) of 
sections of other stages in the fertilization of same eggs. Pre- 
pared by Dr. Edward Leaming. 
162. A series of LANTERN SLIDES from the same _ negatives. 
(Dr. Leaming.) 
163-168. CHROMATIN OR HEREDITARY SUBSTANCE. Mode of 
equal distribution to all the cells of the body. From the 
lobster. Iron hematoxylin stain. 
By A. L. Kean (Biological Department, Columbia College). 
Demonstration of five successive stages in the process of in- 
direct division (karyokinesis), as seen in developing sperma- 
tic cells of the lobster. 
163. RESTING STAGE. A resting cell showing the quiescent 
nucleus. The chromatin (stained black) is in unequal masses 
and distributed throughout the nucleus. The nuclear membrane 
is distinct. 
164. SKEIN STAGE. The first phase of activity of the cell prepara- 
tory to division. The nucleus shows the formation of minute 
threads connecting the chromatin elements. This is the so- 
called “ skein stage.” 
165. CHROMOSOME (CHROMATIN RODS) AND CENTROSOMES. A 
cell nucleus in full karyokinesis. The chromatin has become 
arranged into regular bodies (chromosomes) in a central spindle 
plate (equatorial plate). Fine fibres run outwards from the 
chromosomes and are focussed in centrosomes at the two foles 
of the spindles. The cell is now ready for division. The 
chromosomes will divide first and pass towards the spindle 
poles. 
166. DIVISION OF CHROMOSOMES (CHROMATIN RODS)—SPINDLE 
STAGE. A cell showing the first stage of division. The chro- 
mosomes have divided and appear as two parallel bands in the 
centre of the spindle (see below 12). 
167. DIVISION—MIDDLE STAGE. A cell showing the later stages 
of division. The spindle fibres are disappearing and the cell 
itself is beginning to divide. 
168. DIVISION—FINAL STAGE. The final stage in cell division is 
