a 
682 SCIENCE. 
‘hollow of the back.’ The moose-arrows used 
by this tribe have a double barb forward, as in 
the common arrow, while one side is prolonged 
for two or three inches into a series of barbs ; 
and these have the effect of working inward 
with the motion of the animal, if it be only 
wounded. In_ hunting 
eh moose, while these ani- 
mals are crossing the 
streams or lakes, so one 
a of my interpreters said 
ma. s. who had traded among 
them many times, they 
do not hesitate to jump on the animal’s back 
in the river, leaving the canoe to look after 
itself, and despatch the brute with a hand- 
knife. Of course, a companion is needed in 
a canoe to get the carcass ashore, and secure 
the captor’s canoe. 
Small black flies were now commencing to be 
annoyingly numerous, and were added to the 
plague of mosquitoes, that never left us. The 
bars, that were some protection from the latter, 
were of no use against the former. Nearly 
directly opposite the village the perpendicular 
bluffs shown in the first illustration ceased ; 
and from here on, the hills on both sides of 
the river commenced to grow higher and even 
mountainous in character. About thirty-four 
miles beyond the Selkirk a very conspicuous 
mountain stream came in from the south, 
which I named after Prof. A. R. C. Selwyn 
of Ottawa. The river was still very full of 
islands, however, many of which are covered 
with tall spruce, and look very picturesque in 
the almost canon-like river-bottom, the steep 
hillsides being nearly barren of such heavy 
timber. At this time our attention was called 
to a singular phenomenon, while riding on the 
raft, and especially noticeable on quiet, sunny 
days. I refer to a very conspicuous crackling 
sound, which was not unlike that of fire run- 
ning through cedar-brush, and which the men 
attributed to a pelting on the raft from under- 
neath by a shower of pebbles brought up by the 
swift current, and which would have been a 
good-enough theory as far as the sound was 
concerned ; but measurements in these places 
invariably revealed no bottom for a sixteen- 
foot sounding-pole, and, when going over shal- 
lower and swifter water with pebbly bottoms, 
the crackling ceased. It being always in deep 
water of a boiling nature, figuratively speak- 
ing, I attempted to account for it in a manner 
explained by fig. 9. The raft x, drifting with 
the arrow, passes from a shallow to a deep 
stretch of water. The Yukon is very swift (we 
drifted that day, July 16, forty-seven and a half 
[Vou. III, No. 70. 
~ 
geographical miles in eleven hours and fifty 
minutes), and the pebbles, carried forward 
over the shallow part, and reaching a, are car- 
ried forward and literally dropped on a gravel- 
bank at some point forward, as 6; and, water 
being a good conductor of sound, a person on 
a floating craft, during quiet days, would dis- 
tinctly hear this falling, when it would not be 
heard if they were simply rolling along the 
bottom in swifter water. The suddenness 
with which the crackling commenced, and the 
gradual manner in which it slowly died out, also 
help this idea. A series of soundings before 
and after these sounds would have settled this 
theory ; but it occurred so seldom (once or 
twice, or possibly three times, a day in this part 
of the river), that it was impossible to foretell 
it so as to do so, unless one kept sounding all 
day. It was noticed in a much less degree on 
the lower river, but probably would not have 
been observed if previous experience, of a 
Semone OUT 
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OR ai 
CARS GEI 4 
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Fie. 9. 
more marked character, had not brought it 
before us. Some twenty or twenty-five miles 
below the Ayan town, we saw a large black 
bear about halfway up the hillsides of three 
thousand feet altitude, and, not far from this, 
three mountain goats near the summit. A 
number of Ayan graves were seen on the 
banks of the river, resembling, in general, the 
one photographed at Selkirk. 
(To be continued.) 
DEVELOPMENT OF SIPUNCULUS 
NUDUS. 
Dr. HatscueK adds to the list of his valuable 
embryological memoirs a very elaborate and interest- 
ing paper on the development of the gephyrean, 
Sipunculus nudus. 
The cleavage is unequal; and results in the forma- 
tion of about twenty-four cells, of which seven form 
the endoderm, and seventeen the ectoderm. The 
endodermal cells are arranged in three pairs on the 
lower pole of the egg, with an odd cell at the hind 
end. This stage corresponds to a blastula with a — 
single wall of cells enclosing a cleavage-cavity. The — 
odd endodermal cell is the mother-cell of the meso- 
derm, and is called the ‘primary mesoderm cell’ in — 
the following stages. An invaginate gastrula is 
formed; and during this stage the primary mesoderm — 
cell divides, thus giving a pair of mesoblasts at the 
