50 BULLETIN OF THE 



to the distance occupied by about a dozen of the villi. This tact will be 

 of some interest later, when a comparison is made with the conditions in 

 the mature egg. 



In the sections figured on Plate IX. the villous layer has become still 

 thicker and the villi are correspondingly elongated ; they are also some- 

 what farther apart, as well as thicker. 1 The thickness of the individual 

 villi is really greater than that of the spaces intervening between them, 

 but the appearance as seen under the microscope is represented with 

 tolerable accuracy in the figures. The villi of the egg shown in Fig. 3 

 (Plate IX.) have attained a little greater length than those of the other 

 eggs figured, but the egg itself was probably somewhat smaller than the 

 one shown in Plate IX. Figs. 1 and 5. I am not entirely certain of this, 

 because the egg was incomplete, the yolk having all disappeared except 

 a portion directly underneath the villous layer. 



A more advanced condition in the development of the ovum and its 

 membranes is to be seen in Plate VII. Fig. 5. The evidence that this 

 egg is more advanced than those last described is found in its slightly 

 greater size (nearly 0.7 mm.), and also in the increased size and elon- 

 gated condition of the yolk bodies which already occupy all parts of the 

 egg except a peripheral layer. The villous layer has here attained a 

 thickness of 5.5 fx, or about one third its thickness in the mature egg, 

 but the individual villi have not changed perceptibly from the condition 

 in the previous stage, except in regard to length. 



I have no stages between this condition and that which the eggs pre- 

 sent at maturity, but already enough of the egg membranes has been 

 formed to allow several conclusions as to the method of their produc- 

 tion. 



It is to be observed, that immediately before spawning there is no 

 structure, even in the latest of the stages here described, which can be 

 considered the zona radiata ; neither are there at this time any stages 

 older than the one last described, except the mature ova. It seems to 

 me, therefore, perfectly safe to infer that the zona radiata is developed 

 after a large part, if not the whole, of the villous layer has been produced, 

 and that it is wholly formed during the twelve months immediately preced- 

 ing the spawning. From its late production and its position inside the 

 villous layer, as well as its intimate relations to the yolk, it is further to 



1 In Fig. 5 (Plate IX.) they are represented a little too far apart and not quite 

 thick enough, whereas in Fig. 3 (Plate IX.) they have been represented too close 

 together. The granulosa cells in Fig. 5 are too sharply defined, especially on the 

 side toward the villous layer. 



