STUDIES IN MAMMALIAN EMBEYOLOGY. 549 



existence of an annular peripheral mesoblast, directly deriving 

 from hypoblast-cells, is very sweeping. 



Another detail in Fleischmann^s paper (p. 11) to which I 

 will direct attention concerns a difference which he has 

 noticed in the staining properties of splanchnic and of somatic 

 mesoblast-cells in the region of the primitive streak. A 

 similar phenomenon in the cat was observed by Strahl 

 C Arch. f. Anat. u. Phys./ Anat. Abth., 1886, p. 160) for the 

 rabbit, and has been referred to above by myself (p. 514), and 

 figured on PL XLI, figs. 83 and 91. Certain preparations 

 (a. o., figs. 56 and 59) would lead me to believe that there is 

 a more direct connection between this portion of the somatic 

 mesoblast and the superficial layers of the gastrula ridge. 

 Whether the phenomenon has a higher theoretical significance 

 can for the present not be answered ; attention should, how- 

 ever, be directed towards it. In Selenka's sections of the 

 opossum a somewhat similar phenomenon — not, however, 

 noticed in the text as being marked by different staining pro- 

 perties — is figured on PI. XXI, fig. 7, sm. and splm. 



One other point in Fleischmann's paper should be reflected 

 upon, viz. whether his fig. 10, pi. i, in which three layers are 

 figured in a section just in front of the medullary plate, and in 

 which the hypoblast is uncommonly thick and proliferating, 

 might not after all be interpreted as belonging to a region 

 homologous to that of the protochordal plate in the shrew, or 

 of Bonnet^s chorda-entoblast. 



3. Sundry Observations by Different Authors in Support of the 

 Hypothesis of Precocious Segregation of Part of the 

 Hypoblast in Mammals. 



The views here brought forward with respect to the gastru- 

 lation of the Mammalia, which have been fully discussed 

 above, receive independent corroboration from certain facts 

 already passingly alluded to, which were noticed by other 

 observers and by myself in other mammals. I wish to insist 

 somewhat more fully on these observations. 



