554 THREAD- CELLS OF HELTANTHOTDA. 



seen to project themselves from its surface near its tip ; and 

 if the pressure be gradually augmented, many additional darts 

 will every moment come into view. Not only do these organs 

 present different forms in different species, but even in one 

 and the same individual very strongly marked diversities are 

 shown, of which a few examples are given in Fig. 285. At A, b, 

 c, and D, is shown the appearance of the ' Filiferous capsules,' 

 whilst as yet the thread lies coiled -up in their interior ; whilst at 

 E, v, g, h, are seen a few of the most striking forms which they 

 exhibit when the thread or Dart has started-forth. The Thread- 

 cells are found not merely in the Tentacles and other parts of the 

 external integument of Helianthoid Zoophytes, but also in the long 

 filaments which lie in coils within the chambers that surround the 

 stomach, in contact with the Sexual organs which are attached to 

 the lamellae dividing the chambers. These sometimes contain 

 Sperm -cells and sometimes Ova, the two sexes being here divided, 

 not united, in the same individual. — What can be the office of the 

 Filiferous filaments thus contained in the interior of the body, it 

 is difficult to guess at. They are often found to protrude from 

 rents in the external tegument, when any violence has been used 

 in detaching the animal from its base ; and when there is no 

 external rupture, they are often forced through the wall of the 

 Stomach into its cavity, and may be seen hanging out of the mouth. 

 The largest of these Capsules, in their unprojected state, are about 

 1 -300th of an inch in length ; and the thread or Dart, in Cory- 

 nactis Allmanni, when fully extended, is not less than l-8th of 

 an inch, or thirty-seven times the length of its capsule.* 



* For the fullest description of these curious bodies, as well as for much 

 other valuable information upon Zoophytes, see Mr. Gosse's "Naturalist's 

 Rambles on the Devonshire Coast." — Those who may desire to acquire 

 a more systematic and detailed acquaintance with this group, may be 

 especially referred to the following Treatises and Memoirs, in addition 

 to those already cited : — Dr. Johnston's " History of British Zoophytes," 

 Prof. Milne-Edwards's " Recherches sur les Polypes," and his " Histoire 

 des Coralliares " (in the ' Suites a Buffon '), Paris, 1857, Prof. Van Beneden 

 'Sur les Tubulaires,' and 'Sur les Campanulaires,' in "Mem. de l'Acad. 

 Roy. de Bruxelles," Tom. xvii., and his "Recherches sur l'Hist. Nat. des 

 Polypes qui frequentent les Cotes de Belgique," Op. cit. Tom. xxxvi., 

 Sir J. G. Dalyell's "Rare and Remarkable Animals of Scotland," Vol. i., 

 Trembley's "Mem. pour servir a l'histoire d'un genre de Polype d'Eau 

 douce," M. Hollard's 'Monographic du Genre Actinia,' in "Ann. des Sci. 

 Nat.," Ser. 3, Tom. xv., Mr. Mummery, ' On the development of Tubu- 

 laria indivim,' in " Trans, of Microsc. Soc.," 2nd Ser., Vol. i., p. 28 ; 

 Prof. Max. Schultze, 'On the Male Reproductive Organs of Campanularia 

 genicvAata,' in "Quart. Journ. of Microsc. Sci.," Vol. iii. (1855), p. 59; 

 Prof. Agassiz's beautiful Monograph on American Meduspe, forming the 

 third volume of his " Contributions to the Natural History of the United 

 States of America," and Prof. J. R. Greene's " Manual of the Sub- 

 Kingdom Cctlenterata," which contains a Bibliography very complete 

 to the date of its publication. 



