314 ZOOLOGY: J. LOEB 
My first experiments on artificial parthenogenesis were carried out 
on marine invertebrates, sea urchins, starfish, annehds, and molluscs, ^ 
and since it is difficult to raise the normal larvae of such animals to 
the adult stage it seemed hopeless to attempt the task in the case of 
parthenogenetic specimens. Delage^ had the courage to undertake 
it on sea urchins and succeeded in raising two parthenogenetic larvae 
to the adult stage, one of which was far enough advanced to permit the 
recognition of its sex, which was male. 
It seemed more hopeful to make the attempt in vertebrates. Guyer 
had found that by injecting lymph into the unfertilized egg of a frog 
development could be induced and Bataillon found later that the mere 
pricking of the unfertilized egg of the frog with a needle suffices for the 
purpose; although he believes that with the pricking a blood cell must 
be introduced in order to induce 
a normal development of the egg. 
According to my experience the 
essential feature in fertilization is 
an alteration of the surface layer 
of the egg which in my experiments 
was brought about by chemical 
agencies; while in the experiments 
of Guyer and Bataillon on the egg 
of the frog it was accomphshed 
mechanically. It may be stated 
incidentally that this mechanical 
method has failed in every other 
form thus far tried in our labora- 
tory. 
I have now seven parthenogenetic frogs, {Rana pipiens) over a year old, 
produced by pricking the unfertilized egg. The growth of these animals 
was normal and the variations in growth observed were due to differences 
in taking food. This species of frogs apparently requires two years to 
become fully mature, and some of these seven parthenogenetic frogs 
have now grown to more than half their normal size. They are normal 
in every respect as regards appearance and behavior. One of the frogs 
became infected and was killed at the age of ten months; figure 1 gives 
a photograph in natural size. The legs and the abdomen are slightly 
distended as a consequence of the infection. The egg had been pricked 
April 17, 1915, the metamorphosis of the tadpole to the frog stage took 
place August 29. The frog was killed the 26th of February, 1916. 
Some of the surviving frogs are larger than the one photographed. 
