[10] Prepared by adding to a solution of copper sulphate first tartaric acid, and then caustic soda until the blue mixture is clear. It may be obtained from a chemist if the materials are not available.
[11] Note to Teachers.—A general dissection of a frog should be made and exhibited to the class. Detailed instructions for such a dissection will be found in Marshall’s The Frog (Smith, Elder & Co.) or in Huxley and Martin’s Elementary Practical Biology (Macmillan). The frog’s heart continues to beat for some time after the death of the animal, and may be shown as an illustration of the next section of this chapter. Teachers who are unskilled in dissection may obtain prepared dissections, mounted skeletons, etc., from Newmann & Co., 84 Newman Street, London, W.
[12] More detailed instructions will be found in Foster and Shore’s Physiology for Beginners (Macmillan).
[13] The Descent of Man. Cheap edition, 1s. (Murray).
[14] Gilbert White, The Natural History of Selborne.
[15] See Lloyd Morgan’s Habit and Instinct (Arnold), Thompson-Seton’s Wild Animals I have known (Nutt), and Long’s School of the Woods (Ginn).
[16] Darwin, The Origin of Species (Murray). Cheap edition, 1s.
[17] The amnion originates, early in the second day, as a double fold of the yolk-surface in front of the embryo. Similar folds arise round the sides and tail, forming a low wall ([Fig. 187], A); the folds gradually grow over the embryo ([Fig. 187], B) until, during the fourth day, they meet ([Fig. 187], C) and enclose it in a protective transparent bag, containing a watery fluid.
