LIFE-HISTORY OF XHNOPUS LAVIS, DAUD. (oS) 
come to rest in such a position that the cloacal spout of the female becomes applied to 
the anterior end of a shallow median groove on the ventral surface of the male, which 
runs back to the cloacal opening of the male for about three-quarters of an inch. This 
groove is formed by two skin folds over the ventral edge of the pelvic symphysis. The 
ego is passed out, travels rapidly along this groove, over the cloacal aperture of the male 
and directly backwards about 4 inches to the weed held by the outstretched legs of the 
female, where it adheres. The egg has to travel about 5 inches from the female to the 
weed, and is carried this distance in a straight course. This is partly due to the fillip 
it receives from the tumid lips of the cloaca as it passes out, and partly to a backwardly 
directed current in the water, created by gentle swimming movements of the feet of the 
male. The pair immediately swim away, another ege appears in the cloacal spout of 
the female, and the process is repeated. As each egg or group of eggs is laid, a spas- 
modic quiver can be seen momentarily passing over the body of the male, and at this 
time, I have reason to believe, a very small number of spermatozoa are emitted. 
Fertilisation.—The curious method of oviposition resembles in the action of the 
female the spawning of Urodeles and is so unlike that observed in the Phaneroglossa, 
that the question of fertilisation is raised. Quite a number of considerations point to 
the conclusion that each egg is fertilised as it is laid and after it has passed into the 
water, but all attempts to secure spermatozoa in the water as the eggs were laid proved 
unsuccessful, as were also attempts made to observe fertilisation in the living ege. 
One set of observations repeated at different times proves, I believe, that fertilisa- 
tion does occur after or during deposition of the egg, as in other Anura. The eggs 
when attached always have the dark pole below, and within half an hour rotate within 
the egg-membranes, so that the dark pole is above and the light pole below. In 
Xenopus eges which are unfertilised this rotation does not take place at all as a rule, 
or may be incomplete or take an hour or more to complete. ‘This agrees exactly with 
the rotation described in eggs of other Anura with external fertilisation (R. Herrwic, 
03, p. 534). 
Further, there are at each spawning a number of eggs (100-200) which do not 
become attached, presumably by accident, but fall to the bottom of the aquarium. 
It is exceedingly rare to find a fertilised egg among these. This seems to point to the 
conclusion that a very limited number of spermatozoa are emitted, otherwise it is 
difficult to understand why these eggs should not have spermatozoa carried to them in 
a small aquarium with water kept in constant motion by the active pair of frogs. 
Every now and then during spawning an egg is passed which does not pass along the 
ventral groove of the male in the normal manner, and these drop to the bottom. This 
would account for these eggs not being fertilised. It is hardly probable that they are 
all immature eggs; that would not account for them not having been attached, as they 
are in other respects quite normal. One of these ova has been figured in fig. 1, Plate I. 
The Egg-envelopes.—The diameter of the whole egg when laid varies between 2°75 
and 3°0 millimetres. It is surrounded by a layer of transparent jelly-like substance, 
