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nuclei I always saw one nucleolus and in less-developed ones often 
there were two. Probably also in Eunotia the nucleoli which appear 
in the daughter-nuclei graduafly coalesce. 
The primary division-wall, of which mention has been made, is 
a lamella easily soluble in dilute chromic acid. The siliceous shells 
are formed later. I have not found a centrosome in Eunotia. 
Conclusions. 
In Eunotia major Rabenh. the nucleus divides karyokinetically 
just as in other Diatomaceae, a fact established by LAUTERBORN and 
Karsten. In Eunotia major a central spindle (Zentralspindel) also 
occurs, a body which plays an important part in karyokinesis, as 
the above authors have also shown in other Diatomaceae. Well- 
developed chromosomes are not found in Eunotia major. The nuclear 
network forms short bodies of indefinite shape, which crowd round 
the central spindle and form an annular nuclear plate, which divides 
into two annular halves; these separate from each other along the 
ceniral spindle and develop into daughter-cells. 
With regard to the chromosomes, I may say that my results 
agree with those of KreBAnN and Karsten, but not with those of 
LaAurERBORN. He found in Surirella calcarata and other Diatomaceae, 
in the mother-nucleus as well as in the daughter-nuclei, well deve- 
loped long chromosomes, whose number could be ascertained (16 or 
more). KLEBAHN has not been able to see such chromosomes in Rhopa- 
lodia gibba nor Karsten in Surirella saxonica, but as I did in 
Eunotia major they found only a few short thick bodies of various 
shapes which could not be accurately described, and whose number 
was indeterminate. It must be remembered that the results which 
differ were obtained with different species. 
Physiology. — “On a shortening-rejlex’. By Prof. J. K. A. 
WERTHEIM SALOMONSON. 
(Communicated in the meeting of December 28, 1912). 
By the expression shortening reflex I propose to indicate the con- 
traction of a muscle, the ends of which are passively brought 
nearer together. I shall try to prove this contraction to be a real 
reflex, though the primary shortening of the muscle may not be 
the direct cause. 
We shall first consider what happens when any part of an extre- 
