ON THE ORIGIN OF DOUBLE-YOLKED EGGS. 1 79 



although there are at least two possibilities as to the mechanism 

 of their development. Sections show that they are composed 

 entirely of connective tissue, and that they may or may not 

 possess a lumen. Blood vessels are abundant. From these 

 facts, as well as from the total absence of granulosa cells, I 

 conclude that the suspensoria are not modified follicles, but 

 greatly elongated projections of the ovarian surface, tunica 

 albuginea, filled with stroma. 1 



I am not certain how these elongations have arisen. It is 

 conceivable that they are the products of abnormal growth; 

 it is equally conceivable that they are the result of stretching, due 

 to weakness or readiness to flow on the part of the tunica albu- 

 ginea. In a bird in its normal upright position, the sudden 

 development (Riddle, 'n) of a large yolk mass in a given follicle 

 must seriously increase the load sustained by the tunica, and if 

 this for any reason is weak, stretching in these regions might 

 easily result. It is interesting in this connection that all of the 

 follicles with long suspensoria are either well along in their 

 growth periods, or are attached to those that are. Comparative 

 study of the compound follicles, of the branching suspensoria, 

 and of the threads makes me incline definitely toward the second 

 hypothesis. 



Such study not only suggests that all the structures mentioned 

 are the outcome of one and the same process, but also how the 

 more complicated follicles may have originated. B is a good 

 one to begin with. Before dissection the surface of this irregular 

 follicle gave but faint indication of the four completely separate 

 cavities which it contains. Sections of the interfollicular walls 

 show one continuous connective tissue mass bridging the distance 

 from one granulosa to the other. This latter membrane in all 

 the follicles sectioned appears much hypertrophied. It is at 

 least four times thicker than normal and contains quite large 

 intercellular spaces or lacunae. 



How such a complex follicle could have originated can be 



1 This naturally suggests the question whether the enlargements at their distal 

 ends are really follicles, or merely abnormal structures superficially resembling 

 them. The discovery of large yolks with smooth surfaces within these bodies, as 

 well as the presence of fibrosae and granulosae all in proper relation, leaves no doubt 

 that we are dealing with genuine egg follicles. 



