192 THE BIOLOGY OF HYDRA : 1961 



everting thread. Both structures would appear to be for penetration, 

 and both may be the same if Cutress' interpretation is wrong. If, 

 however, Cutress is correct two things would seem apparent. First 

 with such a large structure as Cutress' dart seems to be, the spines 

 of his mastigophore cannot be as large as those figured by Robson 

 (8) nor as seen in Miss Westfall's micrographs because there would 

 not be space for both. In Miss Westfall's unpublished electron 

 micrographs the spines completely fill the shaft, and Cutress 

 figures spines which would appear to be normal, at least as we see 

 them in the light microscope (see ref. 5, p. 132, Fig. 7b and c). 

 Second, it will continue to be confusing if two dissimilar parts 

 of nematocysts have the same name and Picken's use of the word 

 dart has priority. 



Another difficult point in Cutress' work concerns basitrichs. It is 

 his contention that the category of nematocysts Weill ( 10 ) identi- 

 fied and defined as basitrichs are in fact for the most part better 

 assigned to the category microbasic b-mastigophore. Cutress is 

 correct when he notes the difficulty in solving the problem with the 

 light microscope because the basic problem here is to determine 

 whether one is dealing with isodiametric isorhizas or with hete- 

 ronemes with a butt. The magnitude of the difference between butt 

 and thread may be as little as 0.1 microns Cutress notes, and this 

 is not a readily resolvable difference with a light microscope. Cut- 

 ress solves the problem by arbitrarily deciding that when one sees 

 a straight inverted shaft, as in Weill's basitrich, this means the tube 

 of this portion is differentiated as a shaft, is greater in diameter 

 than the thread and that the tube itself is stilfer than the thread. 

 The fact that this portion of the tube, the straight part carrying the 

 armature, may be stiffened and not coiled only because it is packed 

 with spines seems not to have occurred to Cutress. Cutress suggests 

 we restrict basitrichs to certain nematocysts which so far are known 

 only from anthozoans and have no stiffened or straight part in the 

 inverted tube. These nematocysts, as he shows in his Figure 3, are 

 basitrichs in every sense. In our electron microscope work we have 

 examined uneverted basitrichs. The wall of the spined portion is 

 not thicker than the wall of the thread. We cannot comment on 

 diametric relationships since it would be the everted, not uneverted 

 picture which should be examined and we have not done this. These 



