119 



THE External Characters of Pouch embryos of 



Marsupials. 



no. a.-pseudooh/rops dahu. 



By Frederic Wood Jones, D.Sc, F.Z.S., 



Professor of Anatomy in the University of Adelaide. 



[Read June 8, 1922.] 



Plate VI. 



For all the pouch embryos of this interesting form I am 

 indebted to the authorities of the Perth Museum. The 

 animal was first described by Pjofessor Collett in 1895. In 

 1915 it was placed by Matschie in the sub-genus Pseudo- 

 chirops, when that author split up the large Grenus 

 Pseudochirus of Ogilby. Pseudochirops dahli and P. archeri 

 are the only Australian members of the sub-genus, the 

 other seven constituent species being confined to New 

 Guinea. From the external characters of the pouch embryo 

 it would appear to be a particularly interesting form, and 

 one that is undergoing remodelling in response to the 

 demands of a comparatively recent radiation. 



Hair. — Hair is first visible in the 80 mm. stage, at which 

 time the embryo is flesh coloured. The 50 mm. embryo 

 shows no trace of body hair, though the specialized tactile 

 vibriscae are present. When the embryo has reached 105 mm. 

 the body is entirely clothed with short hair, the general 

 colour of which is light brown. The skin of the embryo is 

 free of pigment. 



Ilaii' Tracts. — The hair tracts are charted from male B, 

 Perth Museum, the embryo, which is shown at pi. vi., being 

 105 mm. in total length. Upon the head are numerous 

 definite hair fields arranged in a rather complicated manner 

 (see fig. 1). 



(A) Immediately behind the naked rhinarium a field 

 of short hair shows a^ uniform forward direction; the free 

 tips of the short hairs extend to the superior margin of the 

 naked rhinarium, and to the upper margina of the narial slit. 



(B) Behind this is an area extending backwards to the 

 anterior angle of the eye, and laterally downwards to the 

 mysticial region. In this field the hair is directed forwards 

 and towards the mid-line, so that the areas of the two sides 

 of the snout meet in the mid-line at a hair ridge. This field 



