NEMATOCYSTS 325 



the capsule of the nematocyst is still retained by the cnidoblast. It is under these circumstances that 

 fibrils of the cnidoblast-wall can best be seen. 



The nematocysts of the tentacle of the protozooid appear to migrate into the tentacular heads from 

 the ectoderm around its base. In mature specimens it is only in this region of the protozooid that any 

 nematocysts can be seen, though the larvae are uniformly covered. It is a point of great interest that 

 because the protozooid possesses only a relatively small tentacle, this never reaches that later stage in 

 evolution found in secondary tentacles, where the much greater demand by these enormous tentacles 

 for nematocysts has led to the development of hypertrophied basigasters called ampullae (see p. 355). 

 In most siphonophores the basigaster of the protozooid is indeed smaller than those of the secondary 

 gastrozooids, but in none of the other siphonophores is the contrast in size so great as in Physalia. 



Neither my colleagues, Dr Evans and Mr Macfarlane, nor myself have been able to resolve the finer 

 details of the threads of the nematocysts. There were certainly no spines as large as those indicated by 

 Hardy (1956, fig. 24 f) in any threads which we have examined. I was disappointed in an offer that 

 was made to obtain pictures with an electron-microscope — the only satisfactory way of clearing up 

 this point. 



50 p 



Text-fig. n. Physalia physalis. Nematocyst discharged from a palpon, to show butt or hampe. The spiral bands 

 are not correctly represented. No spines were visible, x 575. 



The nematocysts of the palpons of Physalia appear to differ slightly from those found on the 

 tentacles. I am again indebted to Miss Eleanor Dodge for a sample of nematocysts which she isolated 

 from palpons. With the assistance of Dr Evans and Mr Macfarlane, I was able to measure and make 

 a drawing (Text-fig. 1 1) of a representative capsule. It has a diameter of 20 ju and, unlike those of the 

 tentacles, possessed a butt or hampe at the base of the thread, the diameter of the butt measuring 3 ju 

 and its length 15^. Although we examined nematocysts with a twelfth-inch objective in ordinary 

 light as well as with phase-contrast and dark-ground illumination, none of us could resolve the finer 

 details of the spiral bands on the everted thread. However it was quite clear that there were no large 

 spines on the butt as illustrated by Weill (1934) in his fig. 3436. Weill was not very precise about the 

 place of occurrence of his ' stenoteles ' : he said that they came from the 'stolons gonozooidiques 

 supportant les medusoides', but I can only suppose that he meant the palpons. I estimate that it 

 would take nearly 80,000 of these capsules to inject 1 mg. of toxin into the prey, and about 24,000 of 

 the tentacular capsules. The defensive role of the palpons in Physalia may be important because of the 

 predatory habit of the associated fish, Nomeus gronovii* 



Lane and Dodge found that nematocysts were still reactive after isolation from the tentacle-tissues 

 and 20 weeks of frozen storage. They estimated that 1 g. of packed, wet, 'purified' nematocysts 

 contained approximately 1,058,000 nematocysts. 



* An article by Professor C. E. Lane (Sci. Amer. 202, i960, p. 158) on nematocysts and their toxin, and on feeding 

 reactions, contains some good photographs and a sketch of gastrozooids stimulated by glutathione. Unfortunately the 

 article repeats some old morphological errors. Professor Lane demonstrates the relative immunity of the loggerhead turtle 

 and of Nomeus gronovii. 



