LIFE-HISTORY OF XENOPUS LAVIS, DAUD. 793 
When an object is to be examined under the microscope, a thick piece of glass or 
several thin pieces are laid in the bottom of the trough, the appropriate fluid poured in, 
and the object then placed as close as possible to the cover-glass end of the trough, with 
the surface of the object so placed that by looking through the end of the trough 
horizontally the required view of the object can be obtained. But the same view can 
be seen by fixing a right-angled prism against the cover-glass and examining the 
reflection of the object thrown up vertically from the internal surface of the hypothenuse 
side, and the whole arrangement can be put on the stage of a vertical binocular 
microscope with the objective over the horizontal face of the prism and the reflected 
image enlarged by the use of low powers. With the arrangement shown in Text fig. 1 
it is possible to use a Zeiss A objective. ‘The prism is fixed to the cover-glass with a 
drop of cedarwood oil or castor oil or glycerine. The object is easily moved about into 
any required position while the eyes are at the microscope, as the lower end of the tube 
does not come in the way of the right hand. 
The side views of eggs and the frontal views of larvee figured on the plates were 
drawn with the help of this little appliance. 
Text Fie. 1.—Glass Trough with prism for internal reflection. (Natural size.) 
Before concluding these introductory remarks, I wish to acknowledge very grate- 
fully the help of the artists who have so patiently and carefully carried out my wishes 
in making the illustrations for this paper. A member of the zoology class of 1903, 
Mr Horatio Marruews, kindly provided the drawings of figs. 12, 13, and 14 from the 
living embryos. The rest of the drawings (excepting four) are from the skilful brush 
of Mr A. K. Maxwe tt, whose work I[ have controlled and confirmed throughout. Figs. 
16, 17, 18 and 19 were sketched by myself from the larva as it hatched, and these 
_ sketches have been carefully elaborated, with the help of the identical specimen (killed 
five minutes after hatching), by Mr E. Witson of Cambridge. 
OBSERVATIONS ON BREEDING AND DEVELOPMENT. 
Breeding Halits—My embryological material has all been obtained from speci- 
mens of Xenopus which I have now kept in captivity for seven years, since December 
1896. Spawn was first obtained in February 1899, when the frogs were in the 
Tropical Lily Tank of the Cambridge University Botanic Garden, and a note on the 
