ACCESSORY CHROMOSOME IN A FROG. "JI 



MATERIAL AND OBSERVATION. 



In the spring of 1916, April 7, to be exact, the writer collected 

 a large number of Rana pipiens' eggs from a string of shallow 

 pools near the University campus. The eggs were allowed to 

 develop in the laboratory. The larvae resulting were used for 

 various experimental purposes, but many were kept until after 

 metamorphosis. Throughout the spring, numbers of the larvae 

 were killed at odd times up to the period of metamorphosis, 

 in order to obtain a complete series of stages illustrating the 

 normal course of development of the germ glands. It was in 

 the early maturation stages of the germ cells of the older larvae, 

 that the body simulating the behavior of an accessory chromo- 

 some was first observed. 



The germ glands of the larvae were fixed in Flemming's fluid 

 and also potassium-bichromate-acetic; both fixatives gave excel- 

 lent results. The sections were cut a thickness of 7.5 ^ and 

 stained with iron-alum haematoxylin. A counter stain of congo 

 red and orange G was used, but equally good results are obtain- 

 able without employing counter stains. 



Microscopic examination of the preserved germ glands of the 

 older larvae revealed the odd fact that the animals were of three 

 kinds: males, females, and larvae indifferent as regards sex; 

 i. e., hermaphrodites, the germ glands of which contained both 

 male and female cells. Richard Hertwig has fully described 

 sexually indifferent frog larvae, animals potentially capable of 

 developing into either sex; since his paper first appeared, 

 several other investigators have confirmed Hertwig's findings. 

 In Rana pipiens this indifferent condition appears to be fairly 

 common, and is especially marked in some larvae; the animals 

 retaining their bisexual character, even after metamorphosis, 

 w r hen one or other of the two sexes results. 



Further examination of my material showed that in the case 

 of the female larvae, the maturation processes begin early and 

 usually several weeks before metamorphosis; conversely, in the 

 male, the first maturation changes seldom if ever occur until 

 several weeks after metamorphosis. All stages of the early 

 maturation processes of the germ cells are visible in the glands 

 of female larvae seven to eight weeks of age. 



