Defence among certain Medusce. 347 



the darkening of the water by it have probably the same 

 physiological function as in the Cephalopoda — to protect the 

 attacked animal from its persecutors and facilitate the capture 

 of food-animals.'' 



The character of the " cystons " in a genus of Apolemidte 

 called Dicymhia is described by Hajckel. Each " cormidiura " 

 or cluster of the stem is said to liave in this genus a single 

 deep-red cyston, and the secreted pigment is accumulated in 

 a " head-like terminal expansion of the distal proboscis, and 

 thrown out by a small terminal opening, the anus." 



In Apolemia uvaria *, which often reaches a great size, I 

 have repeatedly observed the so-called " cystons " in speci- 

 mens from Villa Franca. Hpeckel simply mentions the fact 

 that each cormidium of this genus has several cystons, but 

 gives no special description of them. 



The cystons of Ajwlemia are brick-red in colour and easily 

 distinguished from the remaining appendages of the cormidium. 

 Their general relationship to the covering-scales may be seen 

 in my tigure of the axis of the well-known A. uvaria from the 

 Mediterranean. I have not seen them discharge their ex- 

 cretions tj but the intensity of their colour varies in different 

 individuals and in different cormidia on the axis. Although 

 1 have repeatedly watched the well-known " lana di mare " 

 AjJolemia, I have never been fortunate enough to discover 

 one which ejected colouring-matter from these reddish bodies, 

 and have not been able to produce it by an irritation of the 

 animals. 



There is a peculiarity in the tasters of the genus Nanomia 

 which would seem to have a bearing on the discussion of the 

 pigmented bodies of the cystons. 



A. Agassiz, in his description of Nanomia^ called attention 

 to the pigment at the base of the taster of this genus, which 

 he designated as an " oil-globule." He supposed that this 

 body formed the float of the young Nanomia which budded 

 from the parent. From a comparison of this oil- globule with 

 the float of the adult I have shown that a derivation of the 

 young from the adult by budding is improbable. Still oil- 

 globules are very conspicuous structures on the stem of the 

 Nanomia, and have not been observed by me in other genera. 

 Consequently, although the tentacular knobs and most of the 



* The existence of what I have called " uectotasters " or tentacular 

 appendages to the nectostem in Apolemia is not mentioned bj Ilajckel (up, 

 cit.), although it is an exceptional feature in Apolemia. These appendages 

 and the stem which bears the nectocalyces of Apole^nia are easily seen 

 and have been figured and described, Kijlliker speaks of them as the 

 "■ i'uhler zwischen den Schwimmgiockeu." 



t Bull. Mus. Comp. Zool, vol. viii. no. 7. 



