84 FOLLICULAR DERIVATIVES IN VERTEBRATES III 



Changes in the granulosa cells occur simultaneously with 

 those in the ovum. The cells rapidly increase in size. The 

 originally narrow, flat nuclei become larger, more oval in 

 shape and more transparent, and nucleoli make their appear- 

 ance. The cytoplasm of the syncytium absorbs liquid, which 

 causes it to expand. For the time being it remains fairly 

 homogeneous, but when the granulosa cells have changed 

 sufficiently to justify our referring to the formation of 

 corpora lutca, the most typical stage has been reached, namely, 

 the active production of granules within the cytoplasm of the 

 granulosa cells, and the division of the syncytium into single 

 cells. At the same time there is a great increase in the height 

 of these newly-formed cells, and their nuclei become larger 

 and more active. The conversion of the syncytium into 

 single, well-defined granulosa cells points to the fact that a 

 definite function has been acquired. The granules disappear 

 soon after they are formed. They are extruded at the apex of 

 the cell, partly in the form of granules and partly in liquid 

 form, and place themselves between the oolemma and the 

 granulosa. 



The oolemma is fairly thick, and is pierced by numerous 

 small pores lying side by side and radially with respect to 

 the surface of the ovum. Viewed from above they present a 

 sieve-like appearance, and may allow the passage of substances 

 from the granulosa cells. Immediately after the appearance of 

 granulosa cell secretion the first changes occur at the surface 

 of the ovum, beneath the oolemma. The round, clearly 

 defined particles of the yolk are liquefied and fuse into 

 irregular drops (Fig. 65). Simultaneously the oolemma itself 

 is changed. The drops appear, showing a distinct transition 

 from acidophil into basophil cells. As a result, breaches occur 

 in the wall between the ovular and the follicular tissue, so 

 that the cytoplasm of the ovum and the granulosa cells now 

 come into immediate contact with each other. These changes 

 probably do not originate in the ovum itself, but are initiated 

 by the secretion from the granulosa cells. The granules of the 

 granulosa act as it were as a "disintegrating ferment"; they 



