LIFE-HISTORY OF XENOPUS LAVIS, DAUD. oul 
(18) A few cases of branching tentacles in old tadpoles are figured, and it is argued 
from the frequent symmetry of the branching that there is a congenital tendency to 
branch and that the branching is not due to regeneration after injury. The branching, 
if the above view is correct, is evidence in support of the theory that the tentacles 
are external gills of the mandibular arch (pp. 814-816). 
(19) A very curious difference between the behaviour of the dark chromatophores 
of the head and abdomen and those in the distal part of the fin-fold is described. 
The latter expand at night, while the former contract (p. 816). 
(20) The arm is developed in a sac shut off from the gill-chamber. When it is 
protruded it is found that the action of the branchial current is not interfered with as in 
terrestrial Anura and feeding by the branchial current goes on as before (p. 817). 
(21) The external features of the process of metamorphosis are described (p. 817). 
(22) The young frog is found to feed on small Crustacea, chiefly Daphnia, like a 
young Urodele. 
(23) One specimen, a male, was seen to become sexually mature when two years old. 
In this paper very little is said about the internal anatomy of embryos and tadpoles. 
It is hoped that this omission will be made good later. 
Metuops oF PRESERVATION, EXAMINATION, ETC. 
It is not proposed to give full particulars here of all the methods used in this 
investigation. There are, however, one or two new devices which may be useful to 
others and are therefore worth recording. 
The early stages of Xenopus (segmentation, gastrulation) are best preserved in a 
4 per cent. formaldehyde solution, after stripping all the jelly from the vitelline 
membrane. The latter is so close-fitting that it cannot be removed from the living 
egg in these early stages. When the embryo elongates, the vitellime membrane swells 
up and can easily be removed. From this stage onwards the best preservative for 
general purposes is the one formulated below. Of course, for some special stains, 
special preserving fluids are indicated, such as corrosive sublimate for HEIDENHAIN’s 
iron-hematoxylin, and so on. 
The following mixture was made as the result of experiments to discover a killing 
and fixing fluid with the advantages and without the faults of Perenyi’s fluid. As in 
PERENYIS fluid, the basis is strong alcohol, but glacial acetic acid replaces the nitric acid, 
and formalin the chromic acid. The fluid has greater penetrating, fixing, and hardening 
power than PErEnyrs, and it has the same great advantage of not making the yolk hard 
and brittle. The nuclear structures are far better preserved than they are by PERENyI’s 
fluid, mitotic figures are often perfectly fixed, and the embryos and tadpoles of all ages 
are killed almost instantaneously if they are transferred to the preservative with a 
minimum quantity of water. 
Mix 90 c.c. of 70 per cent. alcohol with 3 c.c. of glacial acetic acid. Any 
