No.t.] THE SMALLEST PARTS OF STENTOR. 249 
Postscript. — After sending the above article to the editor 
I had access to Boveri’s recent paper entitled “Ueber die Be- 
fruchtungs- und Entwickelungsfahigkeit kernloser Seeigeleier 
und tiber die Moglichkeit ihrer Bastardirung,” published in 
Bd. II, Heft 3, of Roux’s Archiv fiir Entwickelungsmechantk 
der Organismen, Oct. 22, 1895. Boveri states that the smallest 
dwarf larva which he obtained came from a fragment which 
could not have measured more than ;!, the volume of the intact 
ovum “bei ungiinstiger Rechnung.”  MHis conclusion is: 
“Das Fragment des Seeigeleies bis herab zu einer Grésse von 
ag des urspriinglichen Kivolumens besitzt die formative Wertig- 
keit des ganzen Eies.”’ This is in marked contrast to the 
results of the other authors quoted, none of whom have found 
a figure less than $. The difference may be due in part to the 
fact that Boveri shook the ova before fertilization, while the 
other experimenters performed this or an analogous operation 
after fertilization ; although this does not seem very probable. 
If the exact proportion of the minimal organization mass to the 
whole ovum be a matter of any importance, very great care in 
the estimation of the volumes of dwarf larvae would seem to 
be necessary, taking into account the differences in thickness 
of the layers in dwarf and normal larvae, and also the relatively 
slow increase in volume of the former. 
The figure which I have found for Stentor is but little 
lower than that of Boveri for the animal ovum, and this approx- 
imation suggests interesting comparisons. 
