106 



LECTURE IX. 



the transverse striae which characterise the ultimate fibres of the 

 voluntary muscles in the Vertebrata.* In the integument of the Pelagia 

 he distinguishes an outer epithelium, and beneath this pigmental cells, 

 with small colourless vesicles in their interspaces : each of these vesi- 

 cles contains a spiral filament, the fine extremity of which projects from 

 the surface, and is probably the duct of the gland, which Dr. Wagner 

 conceives to be the organ of the urticating property. He does not 

 find these spiral glands in the Cassiopeia, which does not sting. 



Ehrenberg has detected and figured certain coloured specks («?) 

 placed at definite distances round the margin of the disc of the 

 Cyanaea, which he regards, with much probability, as organs for the 

 special reception of the stimulus of light. He finds each ocellus con- 

 nected with a small ganglion or mass of nervous matter, from which 

 delicate filaments may be observed to radiate, which probably form 

 a nervous circle around the margin of the disc. Nothing more au- 

 thentic has been observed relative to the muscular or nervous systems 

 of the Medusae. These Acalephae, which swim by the contraction of 

 this muscular and vascular margin of their body-disc, have been 

 termed " Pulmogrades." . 



With respect to the Acalephae which enjoy other modes of loco- 

 motion, and especially those that swim by the action of superficial 

 vibratile cilia, very conflicting evidence has been adduced of their 

 nervous system. 



Dr. Grant f has described and figured a double filamentous chord 

 connecting a chain of eight ganglions around that extremity of the 

 Beroe {Cydippe) jnleus {Jiy. 5A; b), from which the two long cirri- 



gerous tentacula (c? d) are pro- 

 truded. Whatever analogy such 

 nervous system may bear to that 

 of the Echinoderms in the cir- 

 cular disposition of the central 

 filaments, and the radiation of 

 nerves from that centre, it has 

 none in regard to its situation, 

 for the mouth of the Beroe («) 

 is at the opposite end of the 

 ^^''"P" body.^ 



Dr. Milne Edwards§ describes and figures part of the nervous 

 system in a larger species of Beroe {Lesueura vitrea) as radiating 



* Loc. cit. 



t Zool. Trans, vol. i. p. 10. PI. 2. fig. 1. 



\ Forbes, in Annals of Natural History, vol. iii. p. 149. 



§ Annales des Sciences Nat. n. s. torn. xvi. p. 206. Vl. 4. 



