MONOGRAPH OF THE EXISTING CRINOIDS. 383 



activity and the formation of the accumulation is indicated by the complete absence 

 of any spatial relation between this structure and either the discharsred spherules in 

 the nucleus or the destained area within the nucleolus. Moreover, the simultaneous 

 appearance of the accumulation and completion of yolk formation is also accom- 

 panied by a complete cessation of the growth of the nucleolus, a growth which, 

 as already noted, shows at earlier stages a remarkablj' constant relation to that 

 of the egg. The inactivity of the nucleolus during the formation of the accumu- 

 lation is further shown by the fact that nucleoli with a large amount of this 

 accumulated material on their surface and, therefore, presumably fixed some con- 

 siderable time after the completion of yolk formation, do not appear to possess 

 less of the basophile cortical substance than do those in which the accumulation 

 is absent. 



The approximately spherical form of the nucleolus and its steady growth, 

 irrespective of the facility with which it parts with the basic stain, indicate that 

 the whole of the nucleolus is formed of a ground substance continuous alike 

 through the basophile and acidophile regions. The fact that the occasional depar- 

 tures from the spherical form are invariably produced by that portion of the 

 nucleolar surface in contact with the destained area, together with the fact that 

 it is from this region the nucleolar discharge invariably takes place, indicate that 

 the capacity for tenaciously retaining the basic stain is accompanied by a con- 

 siderably firmer consistency of this portion of the nucleolar substance. As the 

 loss of this reaction proceeds from within outward the outermost layers of the 

 deeply basophile cortex must possess a considerably firmer consistency than those 

 lying further inward. This condition readily explains the entire absence of any 

 indication of a discharge taking place directly to the exterior from the vacuoles 

 in the cortical region, however peripherally they may be placed, and lends support 

 to the a.ssumption that the vacuoles discharge instead into the more fluid .substance 

 of the faintly staining area, an assumption which is still further suggested by the 

 periodical discharge taking place from the latter. 



The products of the activity of the nucleolus, the formation of which is accom- 

 panied by the appearance of vacuoles in the basophile region and the loss of this 

 basophile reaction, accumulate, therefore, within the nucleolus, the internal pressure 

 of which at the same time steadily increases. AVhen this internal pressure reaches 

 a certain point the firmer cortex of the nucleolus is ruptured at the point of least 

 resistance — that is, at that point on its surface to which the more fluid faintly 

 staining area happens to approach most closely. When this rupture of the cortex 

 occurs the accumulated products of nucleolar activity, partly in the form of a clear 

 fluid, partly as basophile spherules, are discharged from all parts of the nucleolus 

 through the less resisting, more faintly staining, internal region to the exterior. 



The accumulation of products of nucleolar activity which must be present 

 within the nucleolus prior to its discharge is not very evident. The fluid portion is 

 probably contained within the frequently numerous vacuoles in the cortical region 

 of the nucleolus. Only rarely, however, are spherules similar to those discharged 

 to be seen within the nucleolus. This is to be exi)ected, for the spherular form of 

 the discharged material is as much due to the fluid character of the surrounding 



