THE AMPHIBIA OF OKLAHOMA 



Oocytes of many stages of growth and development are found within 

 a single ovary. (See Figs. 2-4.) It is obvious, therefore, that all the oogonial 

 cysts in the preceding period do not advance in development at the same rate, 

 and some oocytes reach maturity long before others. In general, the larger 

 oocytes are found in the center of the ovary, while the less advanced and the 

 very young ones are located near the periphery. 



Only one oogonium of an oogonial cyst continues development. The re- 

 maining oogonia of the cyst become flattened and combine to form the fol- 

 licular membrane, which surrounds the developing oocyte. (See Fig. 1.) The 

 follicular cells have deeply staining nuclei and even more darkly staining 

 nucleoli. Their walls are not visible, but in some places the follicular mem- 

 brane appears to be two or more cells in thickness, judging by the number 

 of nuclei seen. A thick inner membrane closely invests all larger oocytes, 

 but is rarely seen within the follicular membrane of oocytes less than 0.14 

 mm. in diameter. This is the future "vitelline membrane," usually termed 

 at this stage the "zona pellucida." It is anucleate and almost clear in appear- 

 ance. (See Fig. 1.) The presence within the "zona pellucida" of a "zona radi- 

 ata," which is described for some amphibians, is not apparent in the ovaries 

 of individuals of J. crepitans. A suggestion of this layer is found in certain 

 sections, but is so indistinct as to make its existence uncertain. 



Although the membranes remain fairly constant during the year, the 

 cytoplasm and nucleus of an oocyte show striking changes. The cytoplasm of 

 very young oocytes exhibits no differentiation, and cytoplasmic inclusions 

 are apparently lacking. (See Fig. 3.) In later periods of growth, however, 

 "yolk nuclei," described by King (1908) for B. lentiginosHS, are found. These 

 "yolk nuclei" are thickened areas which stain more deeply with heinatoxylin 

 than the remainder of the cytoplasm. When first noted, they are scattered 

 throughout the outer two-thirds of the cytoplasmic portion. At a still later 

 stage, when the yolk has accumulated in the oocyte, the "yolk nuclei" lose 

 their identity. Whether they play a direct role in yolk formation is not certain. 

 King, in her report of Bufo, suggested this might be true, and believed that 

 the "yolk nuclei" are probably developed from the "vitelline bodies" which 

 are found at an earlier stage. She described the latter as small, darkly stain- 

 ing spots in the cytoplasm which multiply by a form of fission. A careful 

 study of sectioned ovaries from specimens of Acris fixed during all months 

 failed to reveal the presence of "vitelline bodies." These are described, also, 

 for the genus Cryptobranchus by Smith (1912). Smith stated that "the disap- 

 pearance of the 'vitelline bodies' at the time of yolk formation suggests a 

 correlation between the two phenomena; but so far as I have been able to 

 observe, the final stages in the disappearance of the 'vitelline bodies' are not 

 closely associated with the formation of yolk granules, nor have I found any 

 undoubted 'yolk nuclei' such as described by King for Bufo." Smith thought 

 that this is not surprising in view of the diverse methods ot yolk-loriiiation 

 found in different amphibians. Whether "vitelline bodies" are actually lack- 

 ing in individuals of Acris, or whether the methods of fixation and staining 

 used tailed to reveal them, cannot be stated. 



