43 



ON A PLATYPUS EMBHYO 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 ma}'- 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 e^g 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 ege'. 



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 



* Caldwelb Phil. Trans. 1887, p. 473. 



