310 CONTRIBUTIONS TO THE NATURAL HISTORY 



*,* The impossibility of adopting a systematic course in describing the Medusae considered in the preceding pages 

 will render their perusal somewhat difficult ; and I deem it, therefore, necessary to indicate briefly the substance of the 

 different paragraphs, in order to faciliate the reading of this paper, and to render references to it less troublesome. 



Scientific interest of Medusae, p. 221. — Full illustrations, — Method of studying, 222. — Mode of preservation, 224. 



Sarsia, 224. — Hydroid Polypi are truly Medusa;, 225. — Descriptions of the lower animals in general, 226. — 

 They should be traced in all their transformations, — Difficulty of identifying European and North American species, 

 227. — Sarsia mirabilis, — Duration of its life, 228. — Sensitive to the density of the medium in which it lives, — Mode 

 of observation, 229. — Physiological importance of the study of such lower animals, 230. — Gradation of structure, 231. 



— Nervous system, 232. — How to use the microscope in these studies, 233. — Forms of Sarsia mirabilis, — How it 

 moves, 234. — Main bulk of the body a gelatinous mass, 235. — Muscular apparatus, 230. — Lower partition, 238. — 

 Nutritive system, — Proboscis, 239. — Chymiferous tubes, — Rapid digestion, 240. — Tentacles, — Connection of the di- 

 gestive cavity and circulatory apparatus, 241. — Homology and analogy of these parts, 242. — Structure of the tentacles, 

 243. — Nettling cells, — Sensitive bulb, 244. — Eye-specks, 245. — Structure of the nervous system, 246. — Distinction 

 between the functions of the lower animals, — central knob rising into the gelatinous substance, 247. — Its analogy to the 

 black organ of Beroid Medusae, — Organs of reproduction, — Anomalies observed in the number of parts in Sarsia, 248. 



— Analogous to the variation in the number of rays in star-fishes, 249. 



HippocRENE, its hydroid form not yet known, 250. — Generic character, 251. — Naked-eyed Medusae constitute a 

 single natural family, 252. — Position of the ovaries, — Eschscholtz's, Forbes's, and Lesson's classifications, 253. — 

 Characters common to all naked-eyed Medusae, 254, 255. — Intimate connection between form and structure, 255. — Leads 

 to the best method of investigation, — Gelatinous disk of Hippocrene, 256. — Movements, and change of form while 

 moving, 257. — Branching tentacles of the mouth, 258. — Structure examined under high powers, 259. — Digestive 

 system, — Mouth, 260. — Tentacles of the mouth, 261. — Digestion, — Changes of form of the digestive cavity, — 

 Radiating tubes, 262. — The fluid circulated not blood nor chyle, but chyme, — Circulation through the tubes, 263. — 

 Special adaptation of the central digestive cavity, 264. — Connection of the vertical and horizontal tubes with the sen- 

 sitive bulb, 265. — How nutrition is efliected, — The nervous cord, 206. — Its structure, 207. — Sensitive bulb and eye- 

 specks, 208. — Analogy of eye-specks with insect-eyes, 269. — Tentacles not pierced, 270. — Nervous plexus, 271. — 

 Doubtful nerves, 272. — Close connection of the tentacles and eye-specks, 273. — Hippocrene svperciliaris, the name for 

 the American species, — Method of studying the muscular system, — Superficial epithelium, 274. — External bundles 

 of contractile cells, 275. — Differences in different aspects, — Action of this muscular apparatus, 276. — Inner vertical 

 bundles, 277. — Secondary muscular bundles, — Contractile fibres, 278. — Their functions, 279. — Difliculties arising 

 from the form of the gelatinous disk, 280. — Complication of parts above the digestive cavity, 281. — Connection of the 

 chymiferous tubes and circular muscles, — Fourth muscular system, 282. — Different from the circular fibres of the main 

 cavity, 283. — Difference of structure of the muscular tissue in different parts of the body, 284, 



Idea! sections, 284. — Hippocrene probably the perfect form of Tubularia, 286. — Several undescribed species of Me- 

 dusae on the shores of Massachusetts, 287. — Eggs of Hippocrene, 288. 



Nemopsis Bachei, a new genus not yet sufficiently investigated, 289. 



TiAROPSis, general form, 289. — Movements, — Tiaropsis is the Medusa form of Campanularia, — Generic characters, 

 290. — Tentacles, — Large eye-specks, — Tiaropsis intermediate between Sarsia and Hippocrene, 291. — Central diges- 

 tive cavity, 292. — Tentacles, — Large eye-specks, 293. — Eye-specks at the base of the tentacles, 294. — .Sexual organs, 

 295. — Muscular system, 296. — Superficial and inner system, — Circular fibres, 297. — Tiaropsis has no representative 

 in Europe, — Ideal section, 298. 



Thaumantias, comparison of the British and North American Fauna of Medusae, 299. — Thaumantias diaphana, fig- 

 ured in wood-cut, — Anolher species noticed, but not yet described, 300. 



Staurophora, 300. — Genus imperfectly characterized by Brandt, 301. — Eschscholtz's family Dcrenieida to be re- 

 jected, — Unphysiological characters assigned to it, 302. — A new species from Boston harbour, — Its motions, 303. — 

 Gelatinous disk, — Muscles, — Extraordinary changes of form, 304. — Tentacles, — Eye-specks, 305. — Assumes some- 



