DAVID B. SLAUTTERBACK 87 



developed have begun to form a circle around the operculum. 

 Notice that it is surrounded by fine filamentous structures which 

 show a repeat period somewhat larger than 300 A. This section is 

 slightly oblique to the plane of the rods so that in the upper left 

 it has passed through the modified ciliary part and in the center 

 and to the right has passed through the cross-striated rootlet. There 

 are 21 of these plus the true cilium. 



In the next illustration you can see the relationship between 

 the rootlet-like structure and the ciliary-like structure of the stiff 

 rod. If you follow the membrane around the ciliary x)art you 

 see that it passes below and peripheral to the upper end of the 

 clearly cross-striated rootlet. It is remarkable that the rootlet which 

 in the ordinary cilium is supposed to lend structural and function- 

 al stability, should be offset in this way. Though there is little evi- 

 dence to support the notion at this time, such an arrangement 

 might function as a hinge with the ciliary part bending outward 

 and the rootlet remaining fixed.'' 



Figure 34 shows a slightly oblique section through the complet- 

 ed apparatus. Notice the 21 rods and the eccentrically placed 

 cilium. Again the fine filamentous material which interconnects all 

 parts of the apparatus and the operculum. 



The last two micrographs (Figs. 35 and 36) are taken from a 

 section of a very different animal, but I want to use them to illus- 

 trate an important consideration about the functioning of the 

 endoplasmic reticulum in the cnidoblast. It is not evident from the 

 developing cnidoblast that the ril^onucleoprotein granules must be 

 or even can be attached to a membrane of the endoplasmic 

 reticulum in order to function in the synthesis of new protein. It 

 has been argued for some time that only the free granules of ribonu- 

 cleoprotein are active and that after synthesis is completed the free 

 granules move with their product to the endoplasmic reticulum 

 where the product is separated and added to the contents of the 

 lumen of the vesicle. We have seen in the proliferating inter- 

 stitial cells that free granules arc active in the production of protein 

 "for domestic consumption," i.e. new protoplasm. In the case at 

 hand we have a secretory cell in the gut of a small earthworm. 



•"'It should be pointed out that the tubules illustrated in Figures 8 and 17 appear 

 to be continuous with the rootlets of the stiff rods. 



