568 THE POPULAR SCIENCE MONTHLY 



FERTILIZATIOX AND ARTIFICIAL PAETHEXOGENESIS 



OF THE EGG 



By Dr. J. F. McCLENDON 



UNIVERSITY OF MINNESOTA MEDICAL SCHOOL 



TICHOMIEOFF, in 1886, was the first to use tlie term artificial 

 partlienogenesis, referring to acceleration in tlie development of 

 the naturally parthenogenetic eggs of the silkworm by metliods found 

 effective in hastening development in fertilized eggs of the same species. 

 To-day tlie term is applied to development of eggs not usually par- 

 thenogenetic, although a few such might develop in nature under acci- 

 dentally abnormal conditions. 



The exact extent of development that is to be dignified by this term 

 is a matter of dispute, some claiming it should be possible to produce 

 an adult rej^roductive organism by artificial parthenogenesis. Though 

 Delage obtained two sea urchins in this manner and more than one 

 observer has so produced frogs, none of these reproduced a second gen- 

 eration, a fact not hard to understand on remembering that normally 

 fertilized eggs of many animals have never been reared to maturity and 

 reproductive activity under observation. Loeb considers a swimming 

 larva to be the goal of the investigator. But it is interesting to note 

 that the "swimming larvse" of the marine worm Chcetopterus, which 

 he produced from unfertilized eggs, were shown by F. Lillie to be ab- 

 normal, unsegmented or poorly segmented eggs that had developed cilia. 



We may consider for a moment what signifies development in the 

 egg. The egg of any animal is in the beginning a single cell and un- 

 dergoes a certain development before normal fertilization. Some ani- 

 mals reproduce parthenogenetically for several generations (t. e., plant 

 lice) and the silkworm eggs, noted before, undergo more or less devel- 

 opment if fertilization fails to occur. The eggs of most animals, how- 

 ever, do not segment (produce an embryo) before fertilization. Though 

 in many of these same species (for example, sea urchin) the eggs 

 (during maturation) undergo before fertilization two very unequal cell 

 divisions, resulting in the formation of " polar bodies," the unfertilized 

 egg is generally considered a single cell, since the " polar bodies " seem 

 to have no further part in the formation of the embryo. The positive 

 sign of development in the mature egg seems to be segmentation. We 

 may therefore consider artificial parthenogenesis to be demonstrated by 

 the segmentation of unfertilized eggs which do not normally segment 

 until fertilized. 



E. Hertwig was the first to observe the seormentation of unfertilized 



