80 THE BIOLOGY OF HYDRA : 1961 



at least a rapidly diffusible one which quickly can reach an equili- 

 brium level within the group of developing cnidoblasts. In my ex- 

 perience these are usually 14 to 18 cells joined in a cluster, 

 from which it is evident that a rapid diffusion rate is necessary to 

 keep them all very closely synchronized. 



This synchrony is illustrated by the pair of interstitial cells in 

 Figure 7. The dense clumps of granules are the chromatin material, 

 and only remnants of the ruptured nuclear membrane persist. 

 These are not two daughter cells in anaphase, they are in late 

 prophase, so the mitoses are quite closely synchronized. When these 

 cells divide for the last time, the diplosome remains near the 

 plasmalemma ( Fig. 8 ) . The remnants of the achromatic figure, the 

 spindle fibers can be seen clearly (S). They appear to be thin 

 tubular structures on the order of 200 Angstrom units in diame- 

 ter. Whether or not these spindle fibers have any progeny, or any 

 remnant left in the fully differentiated cnidoblast, cannot yet be 

 said. The possibility exists, and I shall point out at a later time what 

 I believe to be their fate. 



You will see at "G" in the figure, a large number of vesicles 

 belonging to the Golgi complex. Most of them do not have ribo- 

 nucleo-protein granules upon their surfaces; but some do and still 

 others have granules on one side and none on the other which may 

 be interpreted as supporting the arguments for the continuity be- 

 tween the endoplasm reticulum and the Golgi complex. 



Dr. Fawcett pointed out earlier today that some groups of 

 cells are not joined together by intercellular bridges of the very 

 intricate structure that you have just seen, but rather by simple dis- 

 continuities of the membranes, an example of which appears in 

 Figure 9. It is difficult indeed to argue that these are not artifacts 

 of preparation techniques. But one can only say that they are fre- 

 quently seen, and they appear in cells which otherwise seem very 

 well preserved. However, two of the cells in the micrograph are 

 bound together by an intercellular bridge of the specific type, and, 

 it is not at all uncommon to see both types of continuit}^ within 

 the same cluster. In fact, joining the same two cells together. 



Now when the endoplasmic reticulum begins to appear, we 

 see coincidentally the first appearance of the nematocyst. The 

 reticulum first appears as scattered vesicles in the cytoplasm, 



