ioo6 A MANUAL OF PHYSIOLOGY 



it prepares the uterus for the implantation of the ovum. He con- 

 siders that there is no difference between the true and the false 

 corpora lutea. ' Lutein,' the dried extract of the corpora lutea of 

 cows, is recommended for the treatment of suppressed menstruation, 

 and the troublesome symptoms arising from the premature pro- 

 duction of the menopause by removal of the ovaries. 



The mode of origin of the corpus luteum has given rise to much 

 discussion. Two chief views have been put forward : (i) That it is 

 a structure derived from the connective-tissue wall (theca) of the 

 discharged follicle (v. Baer, etc.) ; (2) that it is developed from the 

 follicular epithelium (membrana granulosa) (Sobotta, etc.). The 

 second view seems to be best established. The granulosa cells 

 enlarge, it is said, without becoming more numerous. In certain 

 animals (guinea-pig), however, mitotic division of cells of the 

 membrana granulosa has been observed (L. Loeb). 



The influence of the ovary on the formation of the decidua has 

 been illustrated in a very interesting way by the investigations of 

 L. Loeb on the artificial production of deciduomata. He has shown 

 that if a number of incisions are made into the uterus of a rabbit or 

 guinea-pig within a certain interval after the cestral period (period of 

 heat), a structure with the histological characters of the decidua 

 develops at each wound. Impregnation does not appear to be a 

 necessary factor, nor even contact of the ovum with the uterine 

 mucous membrane. On the other hand, ovulation, the discharge of 

 an ovum or ova, or at any rate the condition of the ovary associated 

 with this discharge, seems to be indispensable. For extirpation of 

 the ovaries in a large number of guinea-pigs prevented the formation 

 of deciduomata from wounds of the uterus made at the most favour- 

 able period after copulation. The uterus then appears to have an 

 inherent power of responding to such a stimulus as a mechanica 

 injury by the production of a decidual structure, but only under the 

 influence of the ovary. The ovarian factor is probably not nervous 

 but chemical, some specific substance which acts on the uterus being 

 liberated periodically in connection with the sexual rhythm. 



Development of the Ovum. Before fecundation, and apparently 

 as a preparation for it, the ovum is the seat of remarkable changes, 

 similar upon the whole to those seen in the mitotic or indirect 

 division of ordinary cells.* They have been most fully studied in 

 the eggs of certain invertebrate animals. The division of the cell is 

 initiated by changes in the centrosome and attraction sphere. The 

 centrosome divides into two daughter centrosomes. These take up 

 a position one at each pole of the nucleus. Each daughter-centro- 

 some is surrounded by a system of radiating lines or filaments, which 

 are less conspicuous than the chromatin filaments of the nucleus, 

 since they do not stain as these do. Meanwhile the nuclear mem- 

 brane and the nucleoli disappear, or at any rate become indistinguish- 

 able from the rest of the chromatin skein. The skein breaks up into 

 chromosomes, the number of which is constant for a given species, 

 but is not the same in all species of animals. 



The daughter centrosomes or astrospheres are united by meridional 

 achromatic fibres, which form a spindle running through the nucleus 

 from one pole to the other. The chromosomes arrange themselves at 

 right angles (equatorially) to the spindle, and then each chromosome 

 divides longitudinally into two. The halves of the chromosomes 

 now pass toward their respective centrosomes, being perhaps guided 



* For figures illustrating the changes, see any good textbook of Histology. 



