360 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



In this connection a case that came to the writer's attention is of 

 interest. In May, 1921, a young hunter excitedly telephoned the 

 writer that he had an opossum "with 25 young." The next morning 

 this number had dwindled to 12. But the animal was actually taken 

 with double this number. These were, however, of two sizes, the 

 smaller litter about the size of large mice, which were able to escape 

 through the meshes of the wire inclosing the cage. Now, in the 

 hollow log where the animal in question was captured were two 

 females; one of these escaped, doubtless deserting her own brood 

 which were captured with the other litter and their mother. 



This incident is mentioned because of statements in the literature 

 that a female may carry two litters of different ages. It is sug- 

 gested that such cases are to be explained on the theory that one 

 litter is an adopted one. For until the young are weaned and left 

 to lead an independent existence the mother's teats are enormously 

 enlarged and absolutely unfit for any newly born young that might 

 appear (compare, e. g., the teats in figs. 6, pi. 2 and 45, pi. 10). 

 Physiologically, birth during lactation is not to be excluded; but 

 such embryos would be doomed to perish by starvation even though 

 they reached the pouch. 



BIRTH. 



We pass now to a consideration of the birth. As suggested at 

 the opening of this article, very few observations on the birth of 

 marsupials exist. Doctor Michel witnessed the birth in 1849; and 

 his observations ought to have been sufficient to refute the imaginary 

 tales of the uninitiated concerning the phenomenon. The manner 

 in which the extremely miniature young (fig. 6, pi. 2) reached the 

 pouch and became attached to the teats still remained obscure, 

 although Doctor Michel did not think the mother placed the young 

 on the nipples with her lips. 



Actual observation, however, showed the process to be as simple 

 as it is remarkable. For the young reach the pouch without the 

 aid of the mother — these 11-day-old embryos are born into the 

 world with sufficient neuromuscular coordination and sensory re- 

 sponse to clamber from the vaginal orifice into the pouch, find the 

 teat in a maze of hair and attach themselves for a two months' stay 

 at this haven of food and shelter. The writer witnessed this migra- 

 tion. The young appear at the genital opening and after being 

 licked free of liquid and embrj^onic envelops by the mother they 

 climb "hand over hand" into the pouch. Because of the position of 

 the mother during parturition the young must climb upward to reach 

 the pouch. 



In the case under observation 18 young were born. Thirteen are 

 shown at b in figure 6, plate 2. To these were added 5 pouch young 



