Acoustic Function in Pouch Young of the Opossum

Abstract

Pouch young of the opossum were tested for reflex responses to acoustic stimuli, using a litter captured with the mother when they had attained an estimated age of 29 days (40 mm. C. R. length). The tests were begun when the litter was estimated 43 days old (63–64 mm. C. R.). Preliminary tests for vestibular reflexes show that these appear in pouch young of about 41 days (61–62 mm. C. R.), in general agreement with Langworthy. 1 The experiments on acoustic reflexes were begun on 5 young in the brood pouch and attached to the nipples in the normal manner. The pouch was opened only enough to permit observation of the young, the mother being held quietly on her back. Other factors than the acoustic stimuli were eliminated. During the course of the experiment 2 of the young were killed for neuro-histological study of the labyrinth and brain, so the later results were obtained on 3 experimental animals. As controls we used the mother of the pouch young and another litter of 4 free young 146 mm. long (C. R.) at the beginning of the experiments.

Preliminary tests consisted of shrill whistling, sharp handclaps, vibration of a tuning fork at C” and rustling of the straw of the pen. These were applied as close to the pouch young as possible without introducing other factors such as rush of air, etc. A wind instrument known as the “organette”, giving the notes C, E. G, C', E', G', C”, E”, G” and C”', was used in a closer analysis of sounds which elicited reflex responses. The chords C' E' G' C” and E G C' on this instrument were also used. Sustained notes could be produced when desired.