564 
Balls . — Temperature and Growth. 
two of four mercury cups, which are cut in the thick upper end of the 
sheet. I have found this plan of embedding in paraffin to be much superior 
to insertion in a thin rubber tube on account of its greater durability ; some 
of my couples have been in use for over six months, whereas the rubber- 
covered ones used to corrode through after a fortnight, and this durability 
is a great advantage in Cairo, for it takes six weeks to obtain couples 
Fig. 4. General plan of apparatus, showing arrangement of various portions which has 
been found most convenient. 
with which to repair the wreckage of a clumsy day. The wax plate 
takes rather longer to heat up to the bath temperature, but this could be 
avoided by reducing its size and strength. 
The bath stands on the foot of a retort stand, resting on an asbestos 
cushion. On the bar of the stand are fixed clips for holding the paraffin 
sheet, a beaker, and a burner for heating the beaker. The beaker com- 
municates with the bath by a clipped syphon, so that hot water may be 
added to the bath in order to raise its temperature when necessary. A 
