HISTOLOGY: NEM ATOCYSTS 395 



Reproductions of two illustrations showing the fibrils in large and small cnidoblasts are given by Will 

 (1915) and of the small type only by Hyman (1940). The peptic digestion technique has the notable 

 advantage of dissolving away the cnidoblast completely except for these fibrils. Where a pepsin smear 

 is allowed to dry before being placed in the alcohol, violent surface-tension forces accompanying the 

 last moments of evaporation draw the nematocysts together in clumps, often removing them from 

 their 'baskets'. In the mounted preparation intact isolated 'baskets' can thus be studied. The 

 appearance of such a ' basket ', originally surrounding a large isorhiza, is shown in PI. XXVIII, fig. 7. It 

 will be seen that the fibrils, far from tailing-off towards the apex as Will suggests, continue and form 

 an elaborate fibrillar reticulum around a hole through which, in the intact cell, the nematocyst would 

 discharge. The fibrillar ' basket ' in the cnidoblast containing the small type of isorhiza has a similar 

 reticular structure at its apex and resembles the large type except that, as Will shows, the fibrils inter- 

 twine in the basal region forming a single, helically wound stalk. 



The fibrils are thought to be contractile. The effect of magnesium salts and chloretone in preventing 

 nematocyst discharge in an electrical field was attributed by earlier workers (and more recently by 

 Parker and Van Alstyne, 1932) to anaesthesia of these fibrils. The fibrils stain strongly with iron 

 haematoxylin after coagulant fixation in a way similar to muscle fibres. Like fixed muscle, they resist 

 peptic digestion. Whereas chitin and collagen are laid down extracellularly in Coelenterata, muscle is 

 probably always intracellular, like these fibrils. However, if muscular, these fibrils are unique in 

 certain respects, chiefly in their tendency to intertwine in a helical fashion. Attempts to stain the 

 fibrils with Unna's orcein, known to colour elastic tissue, failed completely, though the nematocyst 

 capsules took the stain. While it is possible that the fibrils are indeed muscular and assist discharge in 

 some way, another possible function is worth mentioning: that they serve to strengthen the wall of 

 the cnidoblast and to retain the capsule after discharge has occurred. 'Harpooned' fish have been 

 seen to struggle violently but unsuccessfully after capture by the tentacles. The discharged nemato- 

 cysts are the only means by which the fish is secured to the tentacles. The fibrils in the cnidoblasts are 

 rooted in the mesogloea and may thus prevent the nematocysts (which they enclose) from tearing loose 

 while a captured fish is being carried up to the digestive organs. 



With regard to distribution, Weill correctly states that the tentacles contain numerous large and 

 small isorhizas. They do not form an even series from large to small ; the intermediate sizes are rare. 

 The range of variation in capsule diameters in the material studied was 9-30 // (Weill gives 

 15-40 ft). 



Nematocysts also occur in the gastrozooids (as Huxley, 1859, pi. x, fig. 4, discovered). They tend 

 to occur in groups arranged at regular intervals around the lip region. These nematocysts resemble the 

 small isorhizas of the tentacles and like them lie in cnidoblasts with long basal stalks. In addition to 

 isorhizas, stenoteles occur in the gastrozooids; they are scattered sparsely over the organ. The butt 

 region (Weill's hampe) can be clearly seen in the undischarged capsule. For some reason only one 

 discharged stenotele has been found in the author's material. The everted butt is 14// long and lacks 

 lateral spikes or barbs. Measurements of stenoteles from a gastrozooid give typical diameters of 

 17-19//. The isorhizas in this preparation are 11-15//. 



In the codon-ectoderm, stenoteles occur sparsely, either independently or in small groups. How- 

 ever, in very young specimens of Physalia, this region appears to be much more generously equipped 

 with nematocysts. 



In mentioning the occurrence of stenoteles in the gonodendra Weill was probably referring to the 

 palpons as the specific site. Stenoteles are very abundant in the distal region of the palpons and spread 

 back along one side for a distance of about one-third the length of the whole organ. They are evenly 

 matched for size and achieve diameters of 21-25// (Weill gives 35-40//). 



