60 
ZOOLOGY: J. LOEB 
From the above results it is seen that the melanophores in the skin of 
Amiurus react to direct stimulation by adrenalin. They are also subject to 
nervous control, and this control is mediated through the eye. There is also 
a suggestion of the secretion of a hormone under certain conditions and of 
its influence on the melanophores. 
* Contributions from the Zoological Laboratory of the Museum of Comparative Zoology 
at Harvard College, No. 306. 
FURTHER EXPERIMENTS ON THE SEX OF PARTHENOGENETIC 
FROGS 
By Jacques Loeb 
Rockefeller Institute for Medical Research 
Communicated January 23, 1918 
It seemed necessary to furnish proof that by the methods of artificial 
parthenogenesis not only normal larvae can be produced from unfertilized 
eggs but that these larvae can also develop into full sized normal adults. 
This task is difficult to accomplish in sea urchins and thus far only Delage 
has reported that he has succeeded in raising one parthenogenetic larva of a 
sea urchin to the sexually mature form. 
The possibility of producing artificial parthenogenesis in the eggs of the 
frog by the method of puncture, as demonstrated in the experiments of Guyer 
and of Bataillon, seemed more promising. The writer has made use of this 
method for deciding the question whether such frogs can reach the adult size, 
and determining their sex. He has now raised twenty leopard frogs to an age 
of from ten to eighteen months, and nine of these frogs are still alive. Some 
of these male frogs have reached the full size of the adult male leopard frog. 
We are, therefore, entitled to say that the frogs produced by artificial parthenogenesis 
can develop into adults of full size and of an entirely normal character. 
Loeb and Bancroft 1 tried to ascertain the sex of a parthenogenetic frog 
immediately after metamorphosis but found the gonads in the intermediate 
stage, i.e., testes containing a few eggs, though it was obvious that the frog was 
developing into a male. It was clear that older frogs were needed for the 
decision of the problem of sex. The writer has been able to ascertain the sex 
in nine frogs of the age of from ten to eighteen months, and in all of these the 
ambiguity inherent in the younger frogs had disappeared. He has already 
reported that the first two of these parthenogenetic frogs has normal mature 
testes containing fully developed spermatozoa. 2 No eggs were found in these 
testes. 
The next four frogs examined were also males, so that the problem seemed 
settled when a year ago last summer one parthenogenetic frog, sixteen months 
