ACALEPn^. 167 



the disc of that species. AVill * could discover them only in the 

 generative tentacles of the Cephea, and in the marginal tentacles of 

 the Pohjxenia. When in action the capsule of the thread-cell is first 

 protruded from the skin and the filament afterwards. 



Some superaddition to the thread-cell would seem, however, to be 

 essential to the urticating faculty, since those cells are present in 

 species and parts that do not sting. 



Another kind of cell, analogous to the "dart-cells" of the Hydra, 

 is also present in the Acalephae, and consists of an oval capsule from 

 which a stifi" bristle-like spine protrudes : these do not urticate : 

 they lie in groups in the skin of the disc of the non-urticating 

 species, and are very abundant in the marginal, oral, and generative 

 tentacles of such species. 



The oral tentacles, those, viz. which are continued from the fringed 

 margins of the oral pores in Rhizostoma and Cephea, are productions 

 of the outer membrane or integument, and are solid, as are also the 

 marginal tentacles in the same genera. The short tentacles produced 

 from the membrane depending from the mouth in Mesonenia contain 

 "a central axis made up of large transparent cells, and extending 

 beyond the base of the tentacle into the substance of the membrane." 

 The marginal tentacles in Mesonema, Oceania, and Cyanaia {fig. 76.) 

 are hollow, and lined by a continuation of the ciliated epithelium of 

 the marginal canal. Tlie large interbrachial tentacles of Cephea are 

 processes of the branched proboscides and have the same structure, 

 consisting of a thick transparent outer substance and an inner mem- 

 brane inclosing a tubular canal : but at the extx-emity they are 

 thickened, and the outer wall is raised into a number of small pyri- 

 form processes. The central canal branches into a kind of plexus which 

 occupies the interior of the enlarged end of the tentacle. In the 

 smaller tentacles which depend from the concavity of the pro 

 boscidian base the central canal terminates in a simple blind end.f 



and drags after it a long train of riband-like arms, and seemingly interminable 

 tails, marking its course when the body is far away from us. Once tangled in its 

 trailing " hair," the unfortuTiate, who has recklessly ventured across the graceful 

 monster's ])ath, too soon -m-ithes iu prickly torture. Every struggle but binds the 

 ]>oisonous threads more fimily round his body, and then there is no escape : for, 

 when the winder of the fatal net finds his course impeded by the terrified Human 

 ■m-estling in its coils, he, seeking no combat with the mightier biped, casts loose 

 his envenomed anns, and swuus away. The amputated weapons, severed from 

 their parent body, vent vengeance on the cause of their destruction, and sting as 

 fiercely as if their original proprietor itself gave the word of attack." CXLVII. 

 p. 10. 



* CXIV. p. 62. t CXLV. pp. 418—420. 



M 4 



