324 



DISCOVERY REPORTS 



Nematocysts 

 We do not yet know the whole story of the development, transport and thread- devagination of the 

 nematocysts of Physalia. There are two distinct types of nematocyst. Those found in the tentacles have 

 globular capsules and tapering threads or filaments (PI. XXV, fig. 4). The capsules are of two mean 

 sizes, 26-8// and 11-3 fi in diameter (Lane and Dodge, 1958). That the threads taper can be seen both 

 in optical section of the coiled-up threads and in devaginated ones. PI. XXV, fig. 5 shows pads of these 

 isorhizas round the mouth of a gastrozooid. Having no butt or hampe they should be referred to as 

 isorhizas. Developmental stages can be found in the walls of the ampullae, from which they migrate 

 not to the earliest formed pads or heads of the tentacle, but to those that have grown a little 

 They can be seen during passage in the ectoderm of the tentacle-tube or lamella. Will (1909) 

 figured the cnidoblasts of this type of nematocyst, and although I could not resolve all the details of 

 those I have examined, I can confirm his account of them in general (Text-fig. 10). The nucleus and 



004 mm 







A B 



Text- fig. 10. Physalia physalis. Nematoblasts. A, from the ampulla, capsule diameter 27 ft. B, from the ampulla, 



capsule diameter 11 [i. n = nucleus. 



nucleolus of the cnidoblast or mother-cell are clearly visible at the inner end. In immature cnidocysts 

 there is a large, central, homogeneous, hyaline mass at the circumference of which the thread 

 can later be seen developing. Surrounding this central mass is a clearer, transparent substance 

 which presumably forms the capsule wall. In 1926 Will published, without figures, an interpretation 

 of what he thought to be the earliest developmental stages, but there still remains doubt about the 

 details.* Chun (1892) had published figures of immature, tentacular cnidoblasts which show the 

 'tube externe', a feature that was puzzling until Weill (1934) showed that it was only the prematurely 

 devaginated thread of an immature nematocyst. In many immature cnidoblasts I have seen the 

 thread of the nematocyst partially devaginated in coils in the body of the cnidoblast as figured by 

 Chun. The thread of the nematocyst is frequently found in preserved material to be devaginated while 



* In my opinion nothing is known yet about normal nematogenesis in any Cnidarian, except that the nematocyst originates 

 as a homogeneous secretion-mass in an ectodermal mother-cell (nematoblast). 



