232 LOEB— THE CYCLIC CHANGES IN [April 22, 



the tumors grow, but with markedly diminished energy. In both 

 cases, in the case of the tumors as well as of the ovaries, we have to 

 deal with a state of living matter intermediate between its full nat- 

 ural vigor and latent life ; we may regard it a state of partial shock 

 of cells, in which the growth takes place but with a considerable 

 decrease in energy. Besides the changes which I have just described, 

 additional processes of the greatest interest take place in the ovaries 

 of a certain number of animals and it is very probable that these 

 processes usually commence at the period following ovulation and 

 are therefore, in a certain sense, a part of the cyclic ovarian changes. 

 The process I refer to concerns an apparently spontaneous partial 

 parthenogenetic development of ova in the mammalian ovary, an 

 occurrence of which I obtained convincing proof only within the 

 last few^ months. 



Some years ago I described peculiar structures that are found in 

 the ovaries of guinea-pigs, and I expressed the opinion that they orig- 

 inated in the ovarian follicles.^ \'ery soon after I had published my 

 observations, certain considerations suggested to me that these struc- 

 tures owe their origin to parthenogenetically developing ova. 



In as much as at that time I had not yet seen early stages of the 

 structures referred to, I was unable to regard this hypothesis as sufili- 

 ciently founded to warrant publication. I continued, however, my 

 investigations in this direction, and recently I succeeded in finding in 

 two animals the desired early stages. They must be interpreted as 

 embryos developing parthenogenetically within the ovary of the 

 guinea-pig. We see in each case a chorionic vesicle with tropho- 

 blast, and plasmodia and syncytia penetrating into the neighboring 

 tissues. There is present also a structure which is probably to be 

 interpreted as a neural tube. 



Aberrant blastomeres (remnants of dividing ova that failed to 

 participate in the embryonic development) cannot be seen in the 

 ovaries of guinea-pigs, and. inasmuch as the embryonic structures, 

 described in my former communication, are relatively frequent, oc- 

 curring in approximately ten per cent, of all guinea-pigs below the 

 age of six months, and, furthermore, inasmuch as they are situated 



^ Archiv f. niikrosk. Anatomie. Bd. 65, 1905. 



