McAllister—Cytology and Embryology. 629 
completely formed. The knotted appearance shown in this 
figure is due in part at least to the optical effect caused by a 
number of strands crossing in the same vertical plane,—the 
combined effect of these crossings being to allow, less light to 
pass through these areas thus accentuating the effect of dark 
bodies or knots. This effect is of course increased by the fact 
of part of the spirem threads being more or less out of focus. 
The bending of a strand upon itself and the frequent folds and 
kinks all tend stil] further to give the nuclear content the ap¬ 
pearance of a reticulum with conspicuous net knots. 
It is not improbable that in some cases there has been a partial 
solution of the spirem threads by the fixing solution and a sub¬ 
sequent reprecipitation of the dissolved materials. Under such 
circumstances, whenever threads touched one another in crossing 
a knot would perhaps be formed. 
Tangential sections show plainly the leptonema condition and 
in the median sections of the nuclei we can also now make out a 
tangle of more or less uniform strands rather than a mixture of 
very fine irregular anastomosing strands connecting unevenly 
distributed chromatic masses of extremely diverse sizes and 
shapes such as were present in the previous stage. 
In the stage represented in Fig. 10 in which synaptic con¬ 
traction is well begun leptonema strands paired for short dis¬ 
tances are common. Slightly later stages still show this pair¬ 
ing for short distances. They also show diversity in the size 
of the spirem threads. Some are quite thin and others are of 
such size as could be expected from a fusion of the thinner 
strands (Fig. 1 ! 2). These phenomena all suggest the grad¬ 
ual side by side pairing of parts of the thin spirem to form a 
coarse spirem such as appears in parts of Fig. 10. Here a part 
clearly consists of the thin spirem threads. A tangential sec¬ 
tion of the same nucleus shows the thin spirem with suggestions 
of pairing on the right side of the figure (Fig. 11). In other 
parts of the same nucleus the strands are distinctly larger and 
as in the upper central part of Fig. 10 paired strands can be 
distinctly seen extending for some distance. As contraction ad- 
