718 ANATOMY OF VERTEBRATES. 



entry of the ovum into the uterus still remains a matter for 

 observation. The young of both OrnithorJiynchus and Echidna 

 will be described in the chapter on the Mammary organs. 



400. Development of Marsupialia. On the 27th of August 

 (1833), a female Kangaroo (Macropus major), captive in the 

 Gardens of the London Zoological Society, received the male. 

 She stood with her fore-paws off the ground ; the male mounted, 

 more canino, embracing her neck with his fore-paws, and retained 

 his hold during a full quarter of an hour : during this period the 

 coitus was repeated three times, and on the second occasion much 

 fluid escaped from the vulva. The male was removed from the 

 female in the evening of the same day, and was not afterwards 

 admitted to her. On September the 2nd, six days after the 

 coitus, I examined the pouch of the female ; and this scrutiny w r as 

 repeated every morning and evening until the birth of the young 

 Kangaroo had taken place. It happened in the night of October 

 4, thirty-eight days after the coitus. On the morning of the 5th 

 of October, I found the young in the pouch, pendant from the 

 tip of the left upper nipple, of the size and shape shown in fig. 

 606 : it will be described in a subsequent chapter. 



The ovarian ovum, in the Kangaroo, agrees in all essential 



J O * ~ 



points with that of placental Mammalia : the main modification 

 is the greater proportion of vitelline substance, and the smaller 

 proportion of the surrounding fluid in the ovisac. In a female 

 Macropus Parryi, the ovum from the largest ovisac of the left 

 ovarium measured ^-Q th of a line in diameter, the germinal vesicle 

 T i th of a line in diameter. We are at present ignorant of the 

 changes that take place in the development of the ovum between 

 the period of impregnation until about the twentieth day of 

 uterine gestation. At this time, in the great Kangaroo (Ma- 

 cropus major), the uterine foetus, fig. 537, measures eight lines 

 from the mouth to the root of the tail ; the gape of the mouth is 

 wdde ; the tongue large and protruded, fig. 569 ; the nostrils are 

 small round apertures ; the eyeball is not yet wholly defended 

 by the palpebral folds ; the visceral cleft reduced to the meatus 

 auditorius externus is not provided with an auricle ; a posterior 

 cervical fissure was either unclosed, or the delicate cicatrix had 

 given way in the manipulation of the foetus. The fore-extre- 

 mities are the largest and strongest ; they are each terminated 

 by five well-marked digits ; those of the hind legs are not yet 

 developed. The tail is two lines long, thick and strong at the 

 commencement ; impressions of the ribs are visible at the sides of 

 the body : the membranous tube of the spinal marrow T may be 



