43 
ON A PLATYPUS EMBRYO FROM THE INTRA- 
UTERINE EGG. 
By Jas. P. Hill, Demonstrator of Biology, and C. J. Martin, 
M.B., B.Sc. (Lond.), Demonstrator of Physiology, in 
the University of Sydney. 
(Plates ix. -xiii.) 
Introduction. 
The following paper is based on the examination of two embryos 
taken from the intra-uterine eggs of a Platypus. Beyond the facts 
that Monotremes are oviparous and the ovum is meroblastic the 
material collected by Caldwell in 1884 has afforded us very little 
information, and we have thought that a description of a 
Platypus embryo of this stage may not be unwelcome to 
zoologists. In this paper we necessarily confine ourselves to a 
description of the structure of the embryo lying before us. Next 
year, now that we know the exact breeding season of Platypus 
in certain convenient localities in New South Wales, we shall 
endeavour to obtain the stages intermediate between the earliest 
we now possess and the embryo described in this paper. 
The female from the left uterus of which the two eggs were 
taken was shot on 1st October of this year. The general external 
characters of the egg have already been sufficiently accurately 
described.* The eggs were both exactly of the same size and 
spheroidal in shape. The egg shell is, as Caldwell described, of 
an opaque white colour and quite soft, presenting a general 
resemblance to the shell of a lizard's egg. 
The eggs measured 18 mm. in their long and 13*5 mm. in their 
short diameter. They are thus somewhat larger than the eggs 
secured by Caldwell, who gives the measurements of the egg when 
* Caldwell, Phil. Trans. 1887, p. 473. 
