The Birth-period of Trichosurus vulpecula. gl 



and there is an enormous liver. There is a double ^^op of the in- 

 testine lying in the umbilical cord as in all higher Veitebrates 0- 



In the spinal cord the formation of the posterior fissure is not 

 yet inaugurated. 



The permanent kidney is in course of development and a few 

 contorted tubules are present. The ureters are solid. 



The sex of the embryo is not at all clear and, apparently, is not 

 yet established. The Miillerian ducts are laid down for a short 

 distance. The anus is still closed. 



The foundation or rudiment of the mammary apparatus is obvious 

 as (Fig. 4) a fold of the Malphigian layer of the epidermis on each 

 side. The fold is filled in by horny epiblast, and, thus, is not visible 

 in the entire embryo. The mammary pockets (Klaatsch) are not 

 neî-i'ly so well developed as in the older embryo. 



The skeleton of the hind limbs is pre-cartilaginous (Vorknorpel), 

 and the vertebral centra and neural arches in this region are in much 

 the same condition. The digits of the hind limbs are not clawed, and 

 they are not beyond the condition of those of similar embryos of 

 higher mammals. 



In this embryo, as in the older one also, there is a great contrast 

 in degree of development between the fore and hind quarters of the 

 body. This was long ago noted by Meckel, Owen, and others, and 

 will be commented upon at a later stage. 



Description of the newly-born Specimen. 



Embryo B. Recently born and with obvious remains of umbilical 

 stalk (Fig. 2, PI. 4). Greatest length in the preserved condition 

 15 mm, the head, as shown in the figure, being more raised than in 

 the uterine embryo. N. L. about 12,5 mm, but not easily measured. 



Externally. The head is raised, so that the chin-line is 

 almost at right angles to the line of the ventral surface. The snout 

 is well-marked, and the openings of the nostrils are very prominent. 

 There is no lachrymal groove visible. The lips are fused together 

 at the sides. The mouth is open, and the tongue, which is hollowed 

 dorsally by the pressure of the teat, does not project. The fore-arm 

 is completely pronated. The fingers are well developed and bear 

 strong claws. 



The hind limb shows hardly an appreciable advance on the con- 



1) As originally described in pig- and dog-embryos by Oken. 



ZooL Jahrb. XL Abth. f. Morph. Q 



