151 
In thus bringing forward these two forms to notice I own 
they require a great deal more research; perhaps, then, | 
may hereafter revive attention to them, should I obtain for 
any future observations the fitting opportunity. 
On Crrrain Mertuops which may be Empioyep in the 
INVESTIGATION of the DEVELOPMENT of the Froa’s Kaa. 
By H. N. Mosexey, B.A. Oxon., Radcliffe Travelling 
Fellow. 
At the present period, at which frogs’ spawn is to be 
procured in abundance, I propose to give a short account of 
some methods which may be conveniently employed in the 
investigation of its development, hoping that they may be of 
some use to those interested in the subject. The first point 
is to obtain fresh spawn. ‘This is best effected by catching a 
pair of frogs or toads, and keeping them in a largish vessel of 
water. The spawn should be taken away from the parents, 
and placed in plenty of fresh water as soon as extruded, and 
this water should be changed every day, so long as it is desired 
to preserve the ova or embryos alive. 
The freshly laid ova have a large white spot, due to the 
absence over this opaque white area of the pigment, which 
invests the remainder of the ovum beneath the vitelline 
membrane. ‘The ovum is so attached to its albuminous en- 
velope that when it is floating this spot is always on the under 
side. 
‘About three hours after fecundation appears the first fissure 
in which the segmentation commences.! The process of seg- 
mentation is best observed by placing one or two ova ina small 
watch-glass with water, and examining them with an inch 
objective as opaque objects by reflected light. The periods at 
which the segmentation commences and at which it reaches its 
successive stages, differ considerably, according to temperature. 
The first fissure appears on the dark surface of the ovum, or that 
whichnaturally floats uppermost, and passes through the central 
point of this upper hemisphere. About one hour later appears 
a second fissure at right angles to the first, then comes an 
equatorial one,and so on. If the ovum be turned on its side, 
and a portion of the periphery be brought into focus, and 
carefully watched, a curious undulation of the mass may be 
1 My observations made at Vienna were confined to the ova of Rana 
esculenta and Bufo cinereus. I have taken the times of these stages of de- 
velopment of R. ¢emporaria from Owen’s ‘ Vertebrates,’ vol. i. 
