394 



DISCOVERY REPORTS 



Table 1. Analysis of the gases filling the float in Physalia 

 (previous work summarized from Winter stein, 1921) 



Nitrogen and other gases (%) 

 The remainder 



The remainder 



The remainder, of which 1-18 is argon 



The remainder 

 The remainder 

 The remainder, of which about 1 % is argon 



lose volume after a few hours. Large tanks with circulating water are needed to keep Physalia in good 

 condition. Bigelow kept specimens in this way for up to a week at Woods Hole. Frequent changing 

 of the water in a small tank is laborious and has the disadvantage of disturbing the animals. An 

 attempt to keep specimens in a plastic cage anchored in the bay at Arrecife was unsuccessful as the 

 wave motion battered the animals against the walls of the cage, and damaged their appendages. 



Two samples of gas were collected in tubes by displacement of liquid paraffin, the gas being with- 

 drawn from the float with a syringe and injected into the tubes (capacity about 30 c.c.) equipped with 

 self-sealing rubber diaphragms. The results of the analysis, made two months later by Miss Ann 

 Sweeney of the Department of Physiology, Oxford, together with some earlier records, are given in 

 the accompanying table (Table 1). 



7. Nematocysts 



Weill (1934) describes two sorts of nematocyst in Physalia: atrichous isorhizas in the tentacles, 

 stenoteles in a certain (not clearly specified) region of the gonodendra. The present study has con- 

 firmed the existence of two types of nematocyst, and it is now possible to add some further details on 

 their structure and distribution. 



First, with regard to structure, examination of the discharged filaments of the isorhizas, both large 

 and small types, reveals the presence of small teeth on three spiral ridges. An early illustration by 

 Murbach (cited and reproduced by Will (191 5)) hints at this feature. Hardy (1956, fig. 24E, f) in a 

 drawing based on a preparation by the present author shows the teeth and ridges. Thus it is clear that 

 Weill's description of the isorhizas as 'atrichous' should be amended to ' holotrichous '. PI. XXVIII, 

 figs. 5, 6 show the appearance of the teeth under phase contrast. 



In this investigation a convenient technique for preparing isolated nematocysts from fixed tissue was found to 

 be as follows : The tissue is washed well to remove the fixative. Then it is placed in 1 % solution of pepsin in 

 o-i N-HC1 at 37 C. After an hour or more the tissue is removed and without washing is dabbed gently on a slide. 

 Nematocysts come loose forming a smear. When the smear is nearly dry it is exposed to the vapour of 40% 

 formaldehyde for 5 min. Then it is transferred to 90% alcohol. Staining can be carried out in Unna's orcein or 

 the smear may be carried through to absolute alcohol, cleared and mounted and examined under phase contrast. 

 In the latter case a mounting medium with a low refractive index such as G. Gurr's XAM (R.I. = 1-491) offers 

 certain advantages. 



In many tentacular preparations isorhizas with incompletely discharged filaments were found 

 (PI. XXVIII, fig. 5). Picken (1953) and Robson (1953) should be consulted for a detailed analysis 

 of the process of discharge and the structure of the filament in Corynactis which, like Physalia, has 

 large holotrichous isorhizas. 



An interesting feature of the isorhizas in Physalia is the elaborate fibrillar ' basket ' occurring in the 

 surrounding cnidoblasts. The general appearance of this fibril-complex is well known from Will ( 1 909) . 



