THE AMPHIBIA OF OKLAHOMA 



of yolk-latlen oocytes which remain is smaller, however, in proportion to the 

 many small oocytes present. Those in an intermediate stage of growth are 

 practically lacking. Evacuated follicles are seen in greater numbers than in 

 the ovaries of specimens fixed during July, and a considarable number of 

 oocytes are in some stage of degeneration. 



Discussion 



The foregoing account of the changes occurring monthly in the ovaries 

 of mature female specimens of Acris indicate a definite annual ovarian cycle. 

 A consideration of the changes in the size of the ovaries in proportion to the 

 total body size, the growth of the oocytes, the accumulation of yolk, and the 

 behavior of the various component parts of the oocytes all point to a yearly 

 cycle beginning late in September and ending with the close of the breed- 

 ing season in late August and early September. 



Little change is seen during the year in the membranes of the ovary. 

 The follicular membrane is present during the entire period of growth of the 

 oocyte and is the last remnant of the follicle after the oocyte has escaped. 

 Degeneration and resorption of this membrane occur at the close of the breed- 

 ing season to make room for the new generation of oocytes which start de- 

 velopment in September. 



"Yolk nuclei" are first observed in ovaries of frogs fixed in November. 

 /No formation of yolk spherules is found until January, when there is a slight 

 thickening of the outer region of the cytoplasm. In ovaries of frogs taken 

 during February the oocytes are found to have a definite cytoplasmic differ- 

 entiation, although there is no region of dense yolk. At the time of yolk 

 formation, the "yolk nuclei" lose their identity; it would thus seem that they 

 play a role in the formation of the yolk. 



The exact mode of the formation and the derivation of yolk is a question 

 of speculation and doubt among workers on amphibian forms. King (1908) 

 in her discussion of the problem remarked that "investigators have seemed 

 to show that yolk is derived directly from nucleoli, or from chromatin, or 

 from follicle cells, are all open to t]uestion, and until they have been con- 

 firmed by further research, I shall be inclined to believe that yolk formation 

 is one of the anabolic processes in the cells which, although it is directly or 

 indirectly controlled by the nucleus, does not depend upon the nucleus for 

 its material substance." She wrote further, "It may be that during the earlier 

 stages in the devlopment of the ova 'yolk is present in the cytoplasm in the 

 form of diffused, unstainable fjuid' as Montgomery has suggested, and that 

 this fiuid is first collected into rounded vitelline bodies and later changes into 

 yolk spherules." There is no indication in the study of females of Acris that 

 yolk is derived in any way from the nucleus or from the follicle cells, and 

 although "vitelline bodies" are not found in this material, it seems from all 

 indications that the "yolk nuclei" may in some way give rise to the first yolk, 

 since these nuclei disappear almost completely when yolk formation begins. 



The nuclei of the oocytes of mature specimens of Acris present only one 



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