^{page 435 note *} Cf. Laguesse, Journal de l'Anat., T. 26, 1890

^{page 436 note *} Ber. der Naturforsch. Gesellsch. zu Freiburg, Bd. iv., 1889. Verhandl. d. dentschen Zool. Gesellsch., 1892.

^{page 436 note †} Zool. Jahrhucher Abt. f. Anat., vol. 17, 1903. For a historical account of histogenesis of thymus and references to literature this work may be consulted.

^{page 436 note ‡} For critical review and references, see Kollmann, Archiv f. Anat., 1900.

^{page 437 note *} Complete historical accounts are given by Choronschitzky, Anat. Hefte. Bd. 13, 1900; and Piper, Diss Med., Freiburg, 1902. See also specially Kollmann, Archiv f. Anat., 1900.

^{page 440 note *} It is probable that these are profile sections of the circular disc-shaped forms.

^{page 444 note *} Arch. Ital. de Biol., T. xxix., 1898, and Mem. a. R. Accad. delle Se. di Torino, s. ii. t. xlvii.

^{page 445 note *} Archiv f. path. Anat., vol. 151, 1898. Pappenheim gives a very extensive bibliography. His theses, summarised at the close of his paper, agree in respect of these blood cells closely with those of this paper.

^{page 446 note *} While it is quite legitimate to call the cellular tissue round the gut and on the mass of yolk cells mesenchyme, it is perhaps not strictly correct to use the term as applied to this tissue. I use it in quite a general sense as a convenient word to indicate the young connective tissue. Through the whole larval stages the so-called lymphoid tissue is mesenchyme in this sense, with free cells in its meshes.

^{page 447 note *} Anatomische Hefte, Bd. 8.

^{page 448 note *} See note, p. 464.

^{page 449 note *} I find a remark almost in the same terms as this was made by Zeigler (Arch. mikr. Anat., xxx., 1887), referring to the similar tract in Teleosts. See also Laguesse, loc. cit., p. 364.

^{page 449 note †} Loc. cit.

^{page 452 note *} The sections in which the ahove count was made were behind the liver, a long distance posterior to the point where the hepatic vein joins the cardinal.

^{page 455 note *} Jour, de l'Anatomie et de la Physiologie, T. xxvi., 1890.

^{page 458 note *} Loc. lit.

^{page 458 note †} Gaz. Méd. de Paris, 1879.

^{page 460 note *} Loc. cit.

^{page 460 note †} See paper by Graham Kerr, Proc. Zool. Soc., 1901–2.

^{page 460 note ‡} Arch. Ital. de Biologie, vol. xxvii., 1897.

^{page 460 note §} Cf. Ziegler, loc. cit., 1892, note, p. 21.

^{page 463 note *} Journal of Anat. and Phys., vol. xix., 1885; Archie f. Mikr. Anat., Bd. 28, 1886.

^{page 464 note *} Trans. Roy. Irish Academy, vol. xxx. part iii. p. 168.

^{page 464 note †} I am here assuming that the facts justify me in concluding for a continuous new formation, at least up to the end of phase 2. The statement in the text is perhaps too sweeping. If it were possible to establish that all the colourless cells were derived from the splanchnic mesenchyme, and that they wandered thence, it would be a fact of great significance, as it is derived directly from the primitive hypoblast, and it might be held that the free cells in it were directly derived from that layer. I think this would be a strained interpretation, and difficult to reconcile with the facts described regarding the nephric tract of the somatic mesenchyme, but it is a possibility which must not be overlooked.

^{page 464 note ‡} An objection might here be raised that the nuclei of the polymorphic cells may regain their simple form in the blood, but as there are many polymorphs in the blood this objection would not have much force.