770 CHARLES L. 130ULENGER. 



coiitiuual stream of tliread-cells arebeino' coured fortb. Tbe 



O A, 



majority of tbcse are obviously on tbe way to tboir tentacular 

 batteries^ altbougb occasionally one may wander into tbe 

 velum, as sbowu in Text-fig. 2. 



3. MiGKATiNu Stinging-cells in Otulu Mkdusj;. 



In tbe preceding paragriipb I liave attempted to prove tbat 

 tbe conspicuous bulbous swellings wliicb occur so constantly 

 as tbe bases of tbe tentacles of craspedote Medusa3 bave an 

 impoitant function besides tbat of bearing tbe ocellar sense- 

 organs. In sucb crasjiedote Medus83 as are devoid of teutacle- 

 bulbs, e.g. tbe Tracbomed usa3 and Narcomedusae, we 

 find tbat tbe edge of tbe umbrella is provided with a special 

 tbickened ling of ectoderm, containing stinging-cells, some- 

 times known as tbe " nettle-ring." Further, those forms in 

 which tbe tentacles take tbeir origin some distance from the 

 margin of tbe bell on tbe exumbrellar surface are provided 

 with special bands of iiematocysts, called ])eronia, which 

 connect tbe above-mentioned nettle-ring witli the bases of 

 the tentacles. Tbese facts make it very tempting to assume 

 tbat the marginal ring of nematoblasts replaces tbe ocellar 

 bulbs in function, and reference to the figures of this organ, 

 given by various autbors, seems to show tbat this assumption 

 is probable correct. It is a point Avliich requires special 

 investigation, and I will at present merely refer to the 

 evidence which is at my disposal. 



Tbe Hertwigs' most accurate figure of tbe umbrella edge 

 of Carmarina (6, PL iv, fig. 5)^ shows the nettle-ring to 

 be packed with tbread-cells witbout definite orientation ; at 

 tbe base of the tentacle, however, a number of uematocysts 

 are drawn arranged in such a manner that there can be 

 little doubt tbat they are migrating from the marginal ring 

 to the batteries on the tentacle. I have examined sections 

 tbrough the tentacles of a medusa of the same genus, and 



' I should like to express my indebtedness to Dr. S. F. Hariuer. F.R.S.. 

 for calling my attention to this figure. 



