22 ON TRK BBEBDING OF ORNITHORHYNCHUS IN 1920, 



one to two millimetres in length between the members of each of the other three 

 pairs. 



I have not found three eggs in a nest, but have twice found triplet young. 

 The shells from which the) triplets taken on 3rd October, 1920, were hatched, I 

 found in the nest, dry and flattened as shown on the right of Fig. 6 of Plate II. 

 On relaxing these by soaking them in warm water, they assumed the appearance 

 shown on the left of Fig. 4, Plate II. It is plain from the figure that each egg is 

 adherent to both its neighbours. 



Of the six "clutches" of eggs taken, only two preserved a full outline (Plate 

 II.. Figs. 1, 3), all the others being more or less dented (Figs. 7, 9), while one 

 was so dented that I was doubtful whether it contained a living embryo. This 

 last egg was also very much discolored. After hatching of the young, the shells 

 collapse and become flattened, having the appearance shown in Plate II., Figs. 2, 

 and 8. 



The measurements of the eggs in millimetres arc as follow: — 







Length. 



' Breadth. 



A. 



Single egg . . 





18 



14 



B. 



Twin eggs . . 



•■! 



16 



16 



12 

 12 



C. 



Twin eggs . . 





17 



Hi 



14 



1-1 



D. 



Single egg . . 





17 



13 



E. 



Twin eggs . . 



'■'■) 



16 



17 



| 26 



F. 



Twin eggs . . 



•i 



15 

 16 



! 2 * 



In the case of E and F, the breadth is of the two eggs together. 



The triplets taken on 3rd October died before measurements were made, but 

 the young from the other four nests measured as follows: — 

 G. Twin young 20 mm. 

 H. Twin young. 40 mm. 

 I. Twin young 65 mm. 

 J. Single young 103 mm. 



These measurements were made from the living animals, along the dorsal 

 curvature, from the tip of the snout to 'the tip of the tail. Photographs from life 

 of two pairs of twins, G (Fig. 8), and I. (Fig. 2), and of the single young one J. 

 (Fig. 5) are shown on Plate II. The twins G. I judge to have been very recently 

 hatched, as the egg shells were still soft, and the navel was not closed up, but 

 showed the remains of the yolk-stalk still protuding. On these grounds I think it 

 safe to state that the young Ornithorhynchus is 20 mm. in length at hatching. 

 That there is a fairly considerable variation in the date of laying is shown by 

 the fact that the single young one, J., which was 103 mm. in length, was taken on 

 27th September, and must have been hatched more than a fortnight earlier: while 

 the newly-hatched twins just mentioned were taken on 4th October. 



I took the temperature of the nesting chambers by thrusting in the thermo- 

 meter the moment I broke into them, and blocking the entrance immediately with 

 a piece of sacking. As the chamber was always broken into by carefully break- 

 ing through the guarding plug which the female had placed in the tunnel, I 

 believe that this method, crude as it may appear, would give fairly accurate re- 

 sults. Of eleven temperatures taken, the minimum was 63° F.. and the maxi- 

 mum 67° F. the average being 64.9° F. The average of seven measurements in 



