368 Proceedings of Royal Society of Edinburgh, [july 15 , 
but need not be written down at present, except in abstract as 
follows : — 
w = (54); 
where 
SB = Hg 1 (A + t 7 2/) + Kg 2 (X + i 7 |/) + Lg 3 (X + i 7 )/) i 
+ MJ 4 (X + < w ) + p £ ^(» i +fl + >■ 
Here P and Q are the two fresh constants, due to the integration 
for iv. By these we can give to W any prescribed values for y = 0 
and y = b. Lastly, by (1), with (49), we have 
where 
u 
= Ue i(wi ^mx+qz) 
U = -(— — +^-2b) 
\nii y m / 
Our six arbitrary constants H, K, L, M, P, Q clearly allow us to 
give any prescribed values to each of U, 93, 933, for y = 0 and for 
y = b. Thus the completion of the realised problem with real data 
of arbitrary functions, as described in § 37, becomes a mere affair of 
routine. 
40. Now remark that the (u, v, w) solution of § 34 comes essen- 
tially to nothing, asymptotically as time advances, as we see by (33), 
(34), and (38). Hence the (it, t), it)) of § 37, which rise gradually 
from zero at t — 0, come asymptotically to zero again as t increases 
to oo . We conclude that the steady motion is stable. 
2. Note on the Epiblastic Origin of the Segmental Duct in 
Teleostean Fishes and in Birds. By George Brook, 
F.L.S., Lecturer on Comparative Embryology in the 
University of Edinburgh. Communicated by Prof. Sir 
Wm. Turner, F.B.S. 
Our knowledge of the development of the excretory system in both 
vertebrates and invertebrates is as yet very incomplete, perhaps 
more so than of any other system. Until quite recently the whole 
of the urogenital system of the vertebrates was supposed to be 
derived from the mesoblast. This view received a sudden check 
