39 



The External Characters of Pouch Embryos of 



Marsupials. 



No 3-/SOOOOA/ BARROWENStS. 



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

 Professor of Anatomy in the University of Adelaide. 



[Read April 13, 1922.] 



Of this bandicoot I have so far obtained but three 

 embryonic stages for description. For all these specimens I 

 am indebted to the authorities of the Perth Museum. As 

 opportunities for obtaining further material may be long 

 delayed, and as the three stages (17 mm., 77 mm., 92 mm.) 

 examined are representative of a long cycle of pouch life, it 

 has been thought worth while to record such details as are 

 ascertainable from the study of these specimens. 



Hair. — Hair is evidently late in development, there being- 

 no appearance of general body hair at the 77 mm. stage. In 

 the embryo of 92 mm. the general body hair is developed, 

 and is of the characteristic hispid type and bright tan in 

 colour. 



Hair Tracts. — In general disposition the stiff harsh hair 

 of the 77 mm. embryo exhibits the utmost simplicity. 



With the exception of one field, the whole of the hair of the 

 head, body, and tail slopes uniformly backwards (see fig. 1). 

 The exceptional area, which may be defined as the gular field, is 

 situated beneath the throat, extending from the angle of the 

 mouth to the root of the neck. In this field the hair trend is 

 completely reversed. The anterior convergent region beneath 

 the chin is marked by the interramal papilla and its vibrisca ; 

 the posterior divergent region is situated at the posterior 

 extremity of the base of the skull. The lateral margins of 

 the area are very definite, and they extend backwards from 

 the angle of the mouth practically along the lines of the rami 

 of the mandibles (see fig. 2). 



Upon the limbs the flow is distal and towards the post- 

 axial margin, but in the case of the fore limb a reversal takes 

 place at the post-axial margin between the wrist and the 

 elbow. Hair is continued to the base of the ungual phalanx 

 of both fingers and toes (see fig. 3). 



The sole of the foot is hairy and the arrangement of the 

 hair tracts is very definite. A central divergent area is pre- 

 sent upon the sole opposite the first digit. Behind this point 

 the hair is arranged in two streams running backwards to 

 the heel and towards the mid line. This backwardly-directed 



