230 Reproductive Phenomena m Tasmanian Marsupials. 



is more than probable tbat this amouJits to no more tlian a 

 coalescence of the l)ilaminar ])ortion of the contiguous yolk-sac 

 walls, in spite of Bluntschli's suggestions to the contrary. 

 In Fseudochirus cooki true twins occasionally occur, two 

 embryos, each in its own amnion, being found in one blasto- 

 cyst. I have as yet observed only some three cases, all of 

 advanced embryos, but it is quite possible tbat close scrutiny 

 of my early blastocyst material would yield younger examples. 

 In all cases both embryos were normal. 



This is interesting in view of the observations of Patterson 

 and Harfman, and of the fact that Pseudochirns is the first 

 diprotodont marsupial in which such an observation has been 

 made. A full description of the relations of these twin 

 embryos will shortly appear in another j)iace. 



It 'may be added that the foetal membranes of Pseudochirns 

 are similar to those described for macropods. 'i'he allantois 

 remains as a small vesicle, never coming into organic contact 

 with the chorion. The yolk-sac circulation is quite like that 

 described for other diprotodont marsupials. 



Of Tasmanian diprotodonts I have been able to obtain 

 fairly rt^presentative collections of intra-uterine stages and 

 i)ouch-youiig of two kangaroo-rats — Pvtorous tridactylus and 

 Btttongia cuniculus. Each of these breeds during the winter 

 season, and is frequently found in the traps set for the 

 catching of rabbits. Each possesses four teats in the pouch. 

 H'lwever, but one young is produced at each birth. Potorous 

 exhibits some peculiar and interesting features. 



There is, for example, evidence from the number of corpora 

 lutea that more than one ovum is extruded from the ovary at 

 ovulation. Of these, but one develops normally, the others 

 apparently being converted into concretionary remnants, like 

 those found by Hartman in iJidelphys*. 



On one occasion the examination of the uteri of a newly 

 trapped female of Potorous showed that both were pregnant, 

 a most exceptional occurrence. The uterus of the right side 

 contained a quite young blastocyst, while in the left "was a 

 well-advanced embryo. Although this is the oidy case where 

 I have known both uteri of a single female of Potorous to be 

 pregnant, still, on a number of occasions, I have found an 

 embryo or blastocyst in one uterus associated with the 

 presence of an extremely young pouch-foetus, wliich had 

 ceitaiiily been born not long beloie. These facts certainly 

 sliow tiiat the female of Pot >rous tridactylus is able to take 

 the male at least twice in the same season. 



* Hartraau, C. G. Ivc. cit. (19] G and 1019). 



