234 LORANDE LOSS WOODRUFF 
of this sort from analogy in higher forms, I intended to let the 
two pairs run their natural course, foregoing the desire to examine 
their nuclear condition. In view, therefore, of the incomplete- 
ness of the experiment, it is perhaps unwarrantable to draw any 
results regarding hybridization and infertility, or even the ‘fixity 
of species’ so far down in the animal scale.”” Simpson gives no 
data to prove that these were actually syzygies between the two 
forms, but if they were, it is obvious that they were not fertile. 
Jennings and Hargitt stated that they had been unable to induce 
the two forms to conjugate. 
In view of the fact that, for example, Maupas studied conjuga- 
tion of both P. aurelia and P. caudatum, and Hertwig studied 
conjugation of P. aurelia, and also that Jennings observed con- 
jugation in both his aurelia races and in his caudatum races, it 
is clear that aurelia forms conjugate and caudatum forms con- 
jugate, but there is no positive evidence that conjugation takes 
place between individuals of aurelia and caudatum. 
Macronucleus. The normal macronucleus of aurelia was de- 
scribed by Hertwig and Maupas and that of caudatum agrees 
very closely. It is an ellipsoidal body with a smooth contour, 
except for a slight depression, in which the micronucleus is usually 
located. But the form of the macronucleus of both aurelia and 
caudatum frequently departs very greatly from the ‘normal’ 
condition. It is not unusual to find paramaecia of my aurelia 
cultures with the macronucleus resolved into several parts. These 
parts apparently may be gathered together into a typical nucleus 
for division, or the cytoplasm and micronuclei may divide, the 
macronuclear fragments which are in the posterior part form- 
ing the macronucleus of one daughter cell and those in the 
anterior part forming the macronucleus of the other daughter 
cell. I shall reserve the full discussion of these interesting 
changes for a special paper. It is- important to emphasize 
the fact that these are not pathological conditions, since the 
general vitality, as indicated by the rate of division, is not 
appreciably affected. 
