86 THE BIOLOGY OF HYDRA : 1961 



and has often been described here, by silver stains, as a dense body 

 in the basal part of the cnidoblast, but I believe it is simply an inac- 

 tive Golgi complex. Immediately below it are very fine filaments 

 which by newer techniques appear to be fine tubules (see Fig. 17). 



Figure 28 is a fortuitous section through a stenotele which is 

 fully developed. The parts of the nematocyst are readily recog- 

 nizable including the operculum (O), two of the three spines, 

 and the faintly striated tubule. The membrane surrounding 

 this structure is quite obvious. The cilium with its basal granule and 

 one of the "stiff rods" are also prominent. Now I think it's obvious 

 that this so-called stiff rod is very similar to the cilium in structure, 

 but you can see faint longitudinal striations in the cilium which are 

 absent in the stiff rod. Another structure which appears often in this 

 zone is the multivesicular ( M V ) body which most closely resembles 

 the lysosomes of DeDuve. I should also like to point out that there 

 are very fine filaments visible in this micrograph which are attached 

 to the cilium and to the stiff rods; in more favorable sections they 

 also appear to be attached to the circumference of the operculum, 

 and may serve in the mechanism of firing the nematocyst. 



In Figure 29 is a cross section of a stenotele. In the center of 

 the micrograph the three heavy spines of the base of the tube can 

 be seen; a dense material is gradually accumulating in them from 

 the periphery inward. The peculiarly convoluted material aromid 

 the spines is the base of the tubule itself and the conspicuous cross 

 striation of it has a repeat period of about 150 A; that is, each 

 light line measures about 75 A wide as does each dark line. The fact 

 that this same periodicity is seen in longitudinal section (Fig. 30) 

 suggests that the tubule is composed of a crystalline array of rod 

 shaped molecules. ( I am not able to explain the difference between 

 my measurements and those of Dr. Chapman though it is not impos- 

 sible that they vary with degree of development or dehydration.) 



I am not going to deal extensively with the cnidocil structure 

 at this time, but I would like to make a few additional observa- 

 tions. In Figure 31 you will see that the stiff rods of the cnidocil 

 appear first as a straight row of dense bodies connected by a fine 

 dense line. And at one end of that row of bodies, there is a basal 

 granule of an unmodified cilium (not visible in this section). This 

 cilium can be seen in figure 32 where the stiff rods, now quite well 



