[21] Amphiporus lactiflorius and Nemertes gracilis. McIntosh. Monograph on British Nemertines. Ray Society.
[22] The rachis is stated by Whitman (No. [39]), and other observers to be formed of nucleated protoplasm, but further investigations on this point are still required.
[23] For a list of the genera with and without nutritive cells, vide Brandt, pp. 47 and 48.
[24] Kupffer, Laichen u. Entwicklung des Ostsee-Härings. Berlin, 1878.
[25] For the different views maintained by Foulis, Kölliker, etc. the reader is referred to the writings of these authors. The grounds for the view here adopted will be found in my paper (No. [64]).
[26] Quart. Journ. of Micro. Science, Vol. XX. 1880.
[27] Blomfield, loc. cit., p. 83, states that he has observed this fact in Lumbricus, Tubifer, Hirudo, Helix, Arion, Paludina, Rana, Salamandra, and Mus.