THE FEMALE REPRODUCTIVE ORGANS. 851 



cytoplasm, rich in nutritive material, but it lacks a centrosome, 

 so that it can not multiply. The spermatozoon has also chromatin 

 for a nucleus, and a centrosome or the material which may give 

 rise to a centrosome, but it lacks cytoplasm, that is, food material 

 for growth. It would seem that if the spermatozoon could be 

 given a quantity of cytoplasm it would proceed to develop an em- 

 bryo without the aid of an ovum. This experiment has, in fact, 

 been made by Boveri. Eggs of the sea-urchin were shaken violently 

 so as to break them into fragments. If now a spermatozoon entered 

 one of these fragments, which consisted only of cytoplasm, cell 

 multiplication began and proceeded to the formation of a larva. 

 On the other hand, it would seem to be equally evident that if a 

 centrosome was present in the egg or some influence could be 

 brought to bear upon it to make it form a centrosome it would 

 develop without a spermatozoon. In some animals eggs do nor- 

 mally develop at times without fertilization by a spermatozoon 

 (parthenogenesis), the eggs that have this property probably pre- 

 serving their centrosomes. Loeb* has shown, however, in some 

 most interesting experiments that certain eggs, especially those of 

 the sea-urchin (Strongylocentrotus purpuratus), which normally 

 develop by fertilization with spermatozoa, may be made to de- 

 velop by physicochemical means. His latest 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 hypertonic 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 obtained previously by Morgan. 



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 

 portion to which the egg becomes attached is the decidua serotina, 

 and it eventually develops into the placenta, the organ through 

 which the maternal nutriment is supplied to the fetus. The ovum 

 has made considerable progress in its development before reaching 

 the uterus, having formed amnion and chorion, with chorionic villi. 

 Some of the ectodermal cells in the chorion become specialized to 

 form a group of trophoblastic cells which have a digestive action, 



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

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



