408 » General Notes, [April, 
Dakota, the writer discovered a dam freshly built of mud, and 
coarse, marshy plants. No trees or bushes could be seen any- 
where in the vicinity. It was about twenty-five feet in length, 
thrown across a sluggish stream about half that width. Its level 
top was about four feet higher than the bottom of the channel. 
The dam was not more than half-filled with water.— F. E. Todd. 
TuE WILpD Horse or THIBET.—The celebrated traveler, Prze- 
valsky, on his return from his third great journey in Central Asia, 
brought to St. Petersburg an example of a new species of Equus. 
This was described in 1881 by Mr. J. S. Poliatow as Æ. przeval- 
sky. It has warts on its hind-legs as well as on its fore-legs, and 
has broad hoofs. These characters ally it to the true horse, but 
the long hairs of the tail do not commence until about tHe middle 
of that appendage. It is thus intermediate between the horse 
and the asses, to which category the other known wild species of 
Equus belong. Its mane is short and erect, there is no forelock, 
and no trace of a dorsal stripe. The stature is small, the-legs 
very thick and strong, the head large and heavy, and the ears 
smaller than in the asses. In color, it is whitish gray, paler and 
whiter beneath and reddish on the head, and on the upper part 
of the legs, which are blackish from the knee downward. 
Przevalsky’s wild horse inhabits the great Dsungarian desert 
between the Altai and Tianschan mountains. The Tartars call it 
“ Kertag,” and the Mongols “ Statur.” It goes in troops of from 
five to fifteen, led by an old stallion. It is lively, very shy, with sight, 
smell, and hearing well-developed, so that it is exceedingly diffi- 
cult of approach. It seems to prefer the saline districts, and to 
be able to do without water for long periods. Thus it can only 
be hunted in the winter, when melted snow can be obtained. 
Przevalsky only met with two herds during his whole stay in the 
desert. The only specimen brought to Europe is in the museum 
of the St. Petersburg Academy of Sciences. 
ZOOLOGICAL Notes.—Sponges—Professor W. S. Sollas has 
recently studied the development of Halisarca lobularis from 
specimens obtained at Roscoff. Schulze, whose specimens were 
taken in the Mediterranean, found that the development of the 
young within the parent sponge did not proceed further than the 
formation of the blastula, or at most of an incipient gastrula ; 
whereas in those observed by Sollas the embryo became -muc 
developed within the parent, and the blastula stage was slurred 
over, apparently to economize space. No segmentation cavity 
was observed, but directly a cavity was necessary, the loosely 
aggregated cells of the morula packed themselves closely to- 
gether to form the wall of the unfinished blastula, leaving their 
= overplus in the interior in irregular heaps which subsequently 
~ arranged themselves into a unicellular layer along the line of the 
~ infolding wall of the gastrula. Professor Sollas attributes the 
