978 THE PHYSIOLOGY OF REPRODUCTION. 



cell division, it would develop without a spermatozoon. In some 

 animals eggs do normally develop at times without fertilization 

 by a spermatozoon (parthenogenesis), the eggs that have this 

 property probably preserving their centrosomes. Loeb* has 

 shown, however, in some most interesting experiments that 

 certain eggs, especially those of the sea-urchin (Strongylocentro- 

 tus purpuratus), which normally develop by fertilization with 

 spermatozoa, may be made to develop by physicochemical means. 

 Numerous means for bringing about artificial fertilization have 

 been described. One method is to treat the egg for a minute or two 

 with an acid (acetic, formic, etc.), which causes the formation of a 

 membrane. They are then placed for a certain interval in a hyper- 

 tonic sea water, made by adding sodium chlorid to ordinary sea 

 water. They are then transferred to normal sea water and after 

 an hour or so they begin to multiply and eventually develop into 

 normal larvae. Similar although less complete results were ob- 

 tained previously by Morgan. Experiments of this character 

 would indicate that the spermatozoon brings into the ovum 

 definite substances, which, by chemical or physicochemical means, 

 initiate and control the process of segmentation. Suggestions as 

 to the nature of these substances are at present very hypothetical. 

 Robertson f states that he is able to isolate from spermatozoa a 

 substance which can fertilize the ovum, that is, cause the forma- 

 tion of a fertilization membrane. The substance is not defined 

 chemically, otherwise than to state that it is not a protein nor an 

 enzyme. He proposes for it the name oocytin. On the other hand, 

 F. R. Lillie t claims that fertilization is due to a substance produced 

 in the egg itself designated as fertilizin which acts as an ambo- 

 ceptor binding the sperm by a spermophile group. He conceives 

 that the sperm when thus bound activates the ovophile side chain 

 in the fertilizin, which then causes fertilization. According to this 

 view the egg is really self-fertilizing, the spermatozoon furnishing 

 simply an activating substance, and the function of the sperm can 

 be assumed by the above-mentioned reagents which induce arti- 

 ficial fertilization. 



Implantation of the Ovum. After fertilization in the tube the 

 ovum begins to segment and multiply, and meanwhile is carried 

 toward the uterus, probably by the action of the cilia lining the tube. 

 Upon reaching the cavity of the uterus it becomes attached to the 

 mucous membrane, usually in the neighborhood of the fundus. 

 The membrane of the uterus has become much thickened mean- 

 while, and in this condition is known usually as the decidua. The 



*Loeb, "University of California Publications," 2, pp. 83, 89, and 113, 

 1905. See also Wilson, "Archiv. f. entwick. Mechanik," 12, 1901. 

 t Robertson, "Journal of Biological Chemistry," 12, 163, 1912. 

 JF. R. Lillie, "Science," October, 1913. 



