NOTES AND MEMORANDA. 455 



the blastoderm is already constituted of two layers, the lower of 

 which is the true hypoblast, and gives rise to the epithelium of 

 the alimentary tract, in the formation of which the invaginated 

 sack has no share. According to the authors, the mesoblast 

 grows out from the lips of the blastopore as four masses. Two 

 of these are lateral ; a third is anterior and median, and although 

 at first independent of the epiblast, soon attaches itself to it, and 

 forms with it a kind of axis cord; a fourth mass applies itself to 

 the invaginated sack. The true alimentary canal is formed by a 

 series of folds similar to those in Aves ; but the tail fold is so 

 situated that the invaginated sack lies on the ventral aspect of 

 the hind end of the alimentary tract. The authors suggest that 

 the invaginated sack gives rise to the AUantois, a view which fits 

 in very well with Gasser's recent observations on the primitive 

 streak of Aves, as well as with the presence of a vesicle at the 

 end of the postanal section of the alimentary tract in Elasmo- 

 branchs, and with Kuppfer's own suggestion about the similar 

 vesicle at the end of the alimentary tract in Osseous Fish. 



The head fold of the Amnion is formed very early, and grows 

 over the head before the closure of the cephalic medullary folds. 



F. M. Balfour. 



Eecent Eesearches on Bacteria. — The progress of knowledge 

 with regard to the life-history of Bacteriahas been carefully recorded 

 in the pages of this Journal during the past ten years, sometimes by 

 original memoirs, sometimes by more or less extended notices of 

 foreign publications : — ' The Origin and Development of Bacte- 

 rium Termo," by Fran Liiders, vol. riii, p. 32. 'Spontaneous Gene- 

 ration,' by Professor Dyer, vol. x, p. 333. ' Relations of Torula, 

 Penicillium, and Bacterium,^ by Prof. Huxley, vol. x, p. 355. 

 * Bacteria and their llelations to Putrefaction and Contagion,' by 

 Prof. Cohn, vol. xii, p. 207. ' Natural History of the Vibriones,' 

 by Oscar Grimm, vol. xii, p. 411. ' The Origin of Bacteria,' by 

 Prof. Sanderson, vol xi, p. 323. 'Bacteria and the Germ 

 Theory,' by Prof. Lister, vol. xiii, p. 380. ' Researches on 

 Bacteria' (first series), by Prof. Cohn, vol. xiii, p. 156. 'A 

 Peach-Coloured Bacterium,' by E, Ray Lankester,' vol. xiii, 

 p. 408. ' The Theory of Fermentations,' by Louis Pasteur, 

 vol. xiii, p. 351. 'Bacteria in Malignant Pustule,' by Drs. 

 Frankel and Orth, vol. xiv, p. 288. ' Bacterium Rubescens,' by 

 Wm. Archer, vol. xv, p. 206. ' Bacteria in Disease,' by Dr. 

 Payne, vol. xv, p. 327. 'A Pink-Coloured Spirillum,' by Dr. 

 Klein, vol. xv, p, 381. 'Account of Cohn's Researches into 

 the History of Bacteria' (second series), vol. x vi, p. 259. ' Further 

 Observations on Bacterium Rubescens,' by E. Ray Lankester, 

 vol. xvi, p. 27. 'Account of Cohn's Researches on Bacteria 



