874 THE AMERICAN NATURALIST. [Vol. XXXVIIL 



additions are evidently made at the periphery of the organ at the 

 expense of the ordinary ectoderm cells. But though the older 

 cells are not dividing, there are many of them in which the cyto- 

 plasm at the outer end contains two nuclei, so that we infer that 

 nuclear division has been going on. No mitotic figures are to 

 be found in these cells but there are evidences of amitosis. Fig. 



5 shows three stages of this : in the lower figure the initial con- 

 striction, in the middle one the completion of the division, and in 

 the upper one the two nuclei have moved apart. 



The physiological significance of this organ is indicated by its 

 name. As usual with prosobranchs, the embryo develops inside 

 an mipervious capsule ; consequently it is of great importance 

 that the wastes from its actively developing tissues be kept out 

 of contact with them. This is done by intracellular storage. 

 The barrier of living cytoplasm at the outer end of the cell 

 keeps the cell the better from disintegrating there and the con- 

 tauied material from escaping. This device reminds one of the 

 Icpuloptera and their scales as reservoirs for waste nitrogen dur- 

 ing metamorphosis. 



^ Amitosis here is clearly in accordance with the view that 

 senescence and amitosis are closely related, for these cells are 



