EMBRYONIC MEMBRANES IN MARSUPIAL ANIMALS. 655 



On the Arrangement of the Embryonic Mem- 

 branes in Marsupial Animals. 



By 



H. Caldwell, B.A., 



Fellow of Caius College, and Balfour Student of the University of Cambridge. 



With Plate XLIII.. 



The facts to be mentioned in the following short notice have 

 hitherto been not only imperfectly but erroneously described. 



Since my arrival in Australia I have obtained considerable 

 numbers of early embryos of various marsupial animals. 



Of Phascolarctos cinereus ("Native Bear") I have a 

 very complete series of nearly 100 embryos in all stages from 

 the unsegmented ovum onwards, while of the various kangaroo 

 and wallaby types I have embryos in most of the stages. I 

 shall not deal with the history of the germinal layers or of the 

 general development in the present paper. The descriptions 

 which follow holds especially for Phascolarctos cinereus 

 and Halmaturus ruficollis. 



These species represent two of the main divisions of the 

 Marsupials, viz. (i) the short-faced opossum-like, and (ii) the 

 long-faced kangaroo-like forms. I think it fair to regard the 

 condition found in these as the typical marsupial one. 



Both Phascolarctos and Halmaturos breed twice in each year, 

 producing a single young one on each occasion. Exceptions 

 to this are by no means uncommon, and in one " native bear " 

 I found three blastodermic vesicles in one uterus. 



