SCIENTIFIC SUMMARY. 
213 
obtained by Del Rio near San Onopre, in Mexico. H. Rose has made an 
analysis of it, showing 6-49 per cent, of selenium, 10-30 of sulphur, and 
81-33 of mercury. The specimen exhibited was not from the original loca- 
lity in Mexico, but from the Santa Clara Mine, in Lake County, California, 
near Clear Lake. It was of particular interest, on account of its locality 
being associated with the Cinnabar of California. Lately it has had the 
name of Tiemanite bestowed upon it. 
Crystallised Green-coloured Felspar. — Mr. R. Dinwiddie exhibited to the 
New York Lyceum of Natural History specimens of crystallised Green- 
coloured Felspar, from what is known as the Sea Wall of Mount Desert 
Island, Maine, where it occurs not very commonly in scattered particles or 
cavities. Many of the crystals were remarkably perfect, and appear upon 
superficial examination to be peculiar. The colour in most of them is very 
bright ; often light but brilliant, and frequently not extending throughout 
the crystal. 
MICROSCOPY. 
The Cilia in Mollusks. — A most interesting paper is that of Professor 
Wyman in the “American Naturalist,” in which he describes a series of 
experiments which he recently conducted on this subject. The first of the 
set of experiments were made with water. For these the gills of Unios and 
Anodontas are well suited. Their cilia are quite active, and vibrate in such 
directions, that on the inner gill the motion is from the free edge, and on the 
outer to it — facts which the experimenter should keep in mind. If an inner 
gill is cut away from its attachment and laid on the bottom of a flat dish, its 
cilia acting as legs, it will soon begin to move with its free edge forwards, 
and will in the course of time travel the entire length of the dish. Professor 
Wyman has seen a whole gill move ten inches in four hours. Under similar 
circumstances the outer gill will move with its base or cut edge forwards. 
This difference depends, as will be readily seen, upon the fact that the cilia 
of the two gills vibrate in opposite directions. The result of ten experi- 
ments gave the rate of motion of a piece of gill measuring 12mm. by 14mm.,, 
6mm. a minute. If two cuter gills are laid with their free edges towards 
each other they will at once begin to approach, and it frequently happens 
after meeting that one crawls directly over the other. 
Development of Comatula . — Herr Metschnikoff has lately published, in the 
Bulletins of the Academy of St. Petersburg, a valuable paper on the above 
subject. To his surprise, he found no water-system whatever in this 
Echinoderm, nor could he trace anything in any way homologous to it ; 
also discovered that what constitutes the water-system of adult Crinoids, 
which has always been homologised with the water-system of other Echino- 
derms, is developed in a totally different manner. In the free-swimming 
Comatula larva the bag-like digestive sac is the only organ developed ; it 
becomes the digestive cavity of the adult after the larva attaches itself tc 
the ground. He noticed the tentacles as diverticula of the digestive sac in 
the interior of the larva ; these subsequently force their way through to the 
exterior, at the time when the digestive bag has become further differentiated, 
