361 



impossible in the descriptions of any given type. This dis- 

 advantage has a corresponding advantage, since each type 

 must be described fully without reference to other descrip- 

 tions. More labour is entailed, but maybe a compensating 

 degree of accuracy is attained which may repay the additional 

 work spent on recording by pen or pencil. The anatomical 

 and histological examination of the material submitted to- 

 review must occupy attention later, and subsequent work will 

 be planned so that microscopical and anatomical details may 

 be correlated with the gross form of specimens examined and 

 described in these papers. 



The External Characters of the Pouch Embryos of 

 Trichosurus vulpecula, var. typicus. 



For pouch embryos of the common Phalanger I have to 

 thank especially the authorities of the Perth Museum, and 

 of the South Australian Museum, as well as students of the 

 Adelaide University. Trichosurus vulpecula is still a com- 

 paratively common animal, and material both adult and 

 immature is not difficult to obtain, and from various sources 

 I have collected a series of young specimens which cover 

 practically the whole range of pouch development. 



In the general form of the pouch embryo the initial size 

 of the forelimbs is noteworthy, as is their gradual outstripping 

 by the hind limbs as pouch development proceeds. The great 

 development of the posterior axillary fold is also a con- 

 spicuous feature of the embryo in the later stages of 

 pouch life. 



Hair. — Hair is visible at the 32 mm. R.V. stage (see 

 fig. A, pi. xiv.. Specimen male A, Perth Museum). At 

 the 80 mm. R.V. stage a new growth of secondary hair is 

 developed among the primary hairs, which have now become 

 considerably elongated. By the 100 mm. R.V. stage the 

 hair is distinctly pigmented, the secondary hairs being: still 

 distinct from the primary hairs, which are more highly 

 pigmented than the more recent hairs. Some irregularity is 

 seen in the correlation of hair growth and embryonic length ; 

 thus, though embryo Specimen male A, Perth Museum, has 

 a distinct hair growth at 32 mm., embryo. Specimen male C, 

 Piper, is almost hairless at 65 mm. 



Hair Tracts. — In Specimen male D, Perth Museum, the 

 hair covering was complete, and afforded the most favourable 

 material for determining the hair trends over the entire body. 

 The description of the hair tracts on this specimen has been 

 checked and confirmed by the examination of older and 

 younger examples. 



