90 J, BEARD, 



the embryo is not to be starved, some of its capillaries must be ready 

 to come into function at that epoch i). 



Therefore, in my former tables it would have been more correct 

 to have said "commencement of functional period of allantoic placenta" 

 instead of "formation of allantoic placenta". 



This question, regarding the initiation of the placental nutrition, 

 has been here briefly considered, because one marsupial exists, and 

 others there may be, in which the occurrence of an allantoic placental 

 connection is now known. The results obtained by Hill, the disco- 

 verer of this placenta, are not yet available in extenso, and, though 

 he has kindly furnished me with short accounts '^) of his embryos, I do 

 not feel at liberty to anticipate his work. So much I believe myself 

 allowed to say, that the newly-born Perameles ohesula is over the 

 critical period, and this is proved by, among other things, the circum- 

 stance, that ossification has then set in the lower jaw. 



This fact of the post-critical birth in Perameles ohesula has been 

 mentioned, in order to anticipate a possible objection, that a mar- 

 supial may have an allantoic placenta, and none the less be born at 

 the critical period. The only case known disproves this, and I hold 

 it to be impossible, that it should be so, if the allantoic placenta had 

 a functional period of any length whatever. 



Macropus thetidis — Pouch-specimen. 



Through the kindness and generosity of Dr. Broom, in presenting 

 this interesting object to me, I am enabled to add notes on the degree 

 of organ-development in a specimen somewhat older than the newly- 

 born Trichosurus. Before cutting the object I had hopes, that it might 

 turn out to be as young as the latter, but these proved to be false. 

 Although it presents no very great advance on the older Trichosurus, 

 it is not so near the birth-period as the latter. The umbilical cord 

 had quite disappeared, and the epitrichium, though still present, was 

 not so thick as in the other two. Moreover, it appeared to be being 

 gradually shed. 



1) The duration of the critical period in mammals is proved by 

 the fact, that of all epochs of the development it is the one, of which 

 embryos are most easily obtained from pregnant females taken at 

 random. This duration indicates, so I conceive, that the nutrition is none 

 too abundant, and, that if not starving, the embryo is in a state of 

 semi-starvation. 



2) I have since examined his sections. 



