386 
ASTRONOMY: A. VAN MAANEN 
time of stimulation and that of contraction, and are not influenced by 
ordinary anesthetics. 
The majority of the muscles in a sea-anemone respond quickly under 
the influence of the nerve-net and enter into a state of enduring contrac- 
tion (tonicity). This is as characteristic of a small fragment of an ani- 
mal, provided it contains a nerve-net as well as muscle, as it is of a whole 
animal. So striking is this excessive tonicity in the muscle of sea- 
anemones that it has been assumed to be their exclusive function and 
they have recently been regarded (Jordan) as animals incapable of 
ordinary reflexes. Such a conclusion, however, seems to be too sweep- 
ing. 
If a specimen of Metridium is allowed to expand fully and a small 
piece of meat is placed on its tentacles, the mouth and oesophagus soon 
open and the sides of the column are marked by a few pronounced verti- 
cal grooves. After the food has been swallowed the grooves disappear 
and the oesophagus closes. The opening of the oesophagus is brought 
about by the contraction of the transverse muscles of the mesenteries 
whose action is so precisely associated with the appropriate stimulation 
of the tentacles that it carries with it all the signs of a reflex. It there- 
fore seems clear that among the muscles in sea-anemones there are not 
only independent effectors, and tonus muscles associated with nerve- 
nets, but neuromuscular combinations that exhibit true reflex action. 
The detailed paper will be published in the Journal of Experimental 
Zoology. 
PRELIMINARY EVIDENCE OF INTERNAL MOTION IN THE 
SPIRAL NEBULA MESSIER 101 
By A. van Maanen 
MOUNT WILSON SOLAR OBSERVATORY. CARNEGIE INSTITUTION OF WASHINGTON 
Received by the Academy, June 14, 1916 
Inasmuch as data for the proper motions of stars, determined by 
photographic methods, have been rapidly accumulating since the 
beginning of the century, it may seem strange that the first results for 
nebulae should have been published only in 1915. It must not be for- 
gotten, however, that photographs of nebulae require much longer 
exposures, and that, even with the best plates, the measures are more 
diflicult and less accurate, because of the unsymmetrical character of 
the points and condensations upon which settings must be made, than 
is the case with the round images of stars. A given point in a nebula 
may be bisected quite differently on different plates and the measures 
