705 



A CONTRIBUTION TO THE DEVELOPMENT OF THE 

 COMMON PHALANGER. 



By R. Broom, M.D., B.Sc. 



(Plates XXII. -XXV.) 



It seems at fii"st sight somewhat surprising that so little work 

 has been don© towards the developmental history of Marsupials, 

 considering the important position occupied by this group, and 

 the number of points on which light might be thrown on the 

 structui'e and development of the higher mammals. But doubt- 

 less one of the chief reasons is that marsupials only breed once or 

 at most, I believe, twice a year, and that the periods of gestation 

 ai'e so short that it is exceedingly difficult for even those on the 

 spot to obtain a good collection of intra-uterine stages. As this 

 difficulty will always exist and the chances are rather against any 

 one collector obtaining a large series of intra-uterine stages of 

 certain forms, it seems advisable that those who are in a position 

 should fill up what gaps they can rather than wait till some one 

 is able to give an exhaustive treatise. 



The difficulties in the way of collecting a series of early stages 

 are not so very great in the case of one or two of the larger forms, 

 but in many others they are considerable, and this is the case 

 with the common Phalanger; so that, though it is one of the 

 commonest of marsupials, scarcely anything has been published 

 on its development. Selenka* in 1891 gave an account of some 

 early stages of the ovum, and in 1897 Beardf published an account 

 of two of my embryos — one shortly before birth and the other just 



* Selenka, E., Studien zur Entwickl. der Thiere, Hft. 5. 

 t Beard, J., "The Birth-period of Trichosurus valpecula," Zool. Jahrb.. 

 1897. 



