74 



NATURE 



\Nov. 27, 1873 



Each tentacle originates in a bulbous base with a distinct ocellus. 

 No lithocysts are visible on the margin. The velum is of mode- 

 rate width. 



The manubrium forms a small projection from the summit of 

 the umbrella, and terminates in four rather indistinct lips. From 

 the base of the manubrium three rather wide offsets are sent off 

 at equal intervals into the walls of tlie umbrella. These gradually 

 contract in diameter, and then, as three narrow tubes of uniform 

 diameter, run towards the margin, where they open into the cir- 

 cular canal. The symmetry of the radiating canals is confined 

 to these three primary trunlvs. From their wide pro-ximal ends 

 each sends off branches, some of which may be traced to the 

 margin where, like the three primary canals, they enter the cir- 

 cular canal, while others can be followed for various distances in 

 the umbrella walls, in which they terminate by blind extremities 

 without ever reaching the margin. These branches are very 

 irregular in the number sent off from each primary canal, as well 

 as in their length and directions. 



The generative elements are formed in oval sporosacs deve- 

 loped one on each of the three primary canals at the spot where 

 the wider base passes into its narrower continuation. The 

 ova may be seen within them in various stages of development ; 

 they increase considerably in size before the commencement of 

 segmentation, always showing up to that period a large and dis- 

 tinct germinal vesicle with germinal spot and with a distinct 

 nucleolus in the interior of tlie germinal spot. The development 

 of the ovum proceeds within the sporosac to the segmentation of 

 the vitellus and the formation of the planula, which now breaks 

 through the outer walls of the sporosac and remains for some 

 time adhering to their external surface. The planula differs re- 

 markably from the typical hydroid planula. It remains of a 

 nearly spherical form, never acquiring cilia, and possesses little 

 or no power of locomotion. The gastric cavity, however, is 

 fully formed. The author was unable to follow the ova in their 

 further development. 



The little medusa now described, departs in several im- 

 portant points from the typical hydroid medusa. From this it 

 diflers in the ternary disposition of the primary radiating canals, 

 and in the irregular non-symmetrical arrangement of those which 

 are subsequently formed. Among the very many specimens exa- 

 mined, the author never found any in which the canals had 

 become regular in their disposition, even in those which had dis- 

 charged the contents of their sporosacs, and had evidently attained 

 the term of their existence. It differs also from the typical 

 medusa in the form and non-ciliated condition of the planula ; 

 and still further in the fact that while the generative elements 

 are borne on sporosacs, developed on the radiating canals, the 

 marginal bodies are ocelli and not lithocyst. 



4. — Circe invertins (nov. spec.) 



Among the hydroid medusae captured in the towing-net, were 

 two or three specimens of a species referable to the genus Circe 

 of Mertens. It measures about half-an-inch in its vertical dia- 

 meter, and about a quarter of an inch transversely. It is 

 cylindrical from its base upwards, for about two-thirds of its 

 height, and then contracts abruptly, and arches dome-like 

 towards the truncated summit, which is surmounted by a solid 

 cone of the gelatinous umbrella substance. From the summit of 

 the umbrella-cavity, a solid somewhat fusiform extension of the 

 roof hangs down in the axis of its cavity for »bout two-thirds of 

 its depth, and at its free end carries the manubrium, which ex- 

 tends nearly to the codonostome. The margin of the umbrella 

 carried eighty very short and but slightly extensile tentacles, 

 which were connected at their bases by a very narrow mem- 

 braneous extension of the margin, with rather irregular free-edge. 

 Lithocysts are situated at irregular intervals upon the margin. 

 There are about sixteen of them; they consist each of a minute 

 spherical vesicle with a single large spherical concretion. There 

 are no ocelli. There is a moderately wide velum. 



The radiating canals are eight in number. They spring 

 from the base of the manubrium, run up the sides of the solid 

 process which hangs from the summit of the umbrella ; pass 

 from this to the walls of the umbrella, and then run down towards 

 the margin in order to open into the circular canal. 



The generative elements are borne in pendent sporosacs, which 

 spring from the radiating canals close to the summit of the 

 umbrella cavity. 



The motion of the medusa takes place by means of sudden 

 jerks, reminding us of the way in which certain Diphydse dart 

 through the water. 



The medusa possesses also a very singular habit of partial in- 

 version. This takes place along the line which separates the 

 dome-like portion of the umbrella cavity from the lower cylin- 

 drical portion, and consists in the withdrawal of this dome-like 

 summit and the lower portion oi the cavity. When thus inverted 

 the little animal presents a drum-shaped form, with the manubrium 

 hanging far out of the codonostome. 



Alexander Agassiz considers the genus Circe, of Mertens, as 

 synonymous with Trachytiema Gegenbaur, and points out that 

 the name of Circe had been already used for a genus of mollusca. 

 He further removes it from among the true hydroid medusse, 

 and regarding it as closely allied to the ^Kginidu:, places it along 

 with those in the Ilaplostomece Agassiz, a sub-order of the Dis- 

 cophora. 



The author, however, could not see sufiScient grounds for the 

 removal of Mertens' genus from the true Hydroida, with which 

 the medusa now described agrees in all essential points, includipg 

 the form and disposition of the gastro-vascular and generative 

 systems and the structure of the marginal lithocysts. Neither 

 could he agree with Alexander Agassiz in identifying it with 

 Trachynetna. The greatly developed solid peduncle by which 

 the manubrium in Circe is suspended from the summit of the 

 umbrella-cavity in a way, however, which has its parallel in Tima 

 among others, is of itself a character of generic importance by 

 which Circe must be kept apart from Trachyncma. It is true 

 that Gegenbaur's Trachyncma has the character of a young form, 

 and until we have further evidence of its adult state its affinities 

 cannot be regarded as established. 



Gegenbaur believes that he has established the direct develop- 

 ment of Trachyncma from the egg without the intervention of a 

 hydriform trophosome, but unfortunately we have no data by 

 which to compare in this respect Circe with Trachyncma. 



It must be admitted too that in the imperfect contractility of 

 the marginal tentacles and in the somewhat greater firmness of 

 the umbrella walls the little medusa described in the present 

 communication possesses characters which look towards the 

 ALi^inidiC, but these are by no means sufficiently strong to justify 

 its separation from the ordinary hydroid medusae. 



5.— Tomopteris 



A few young specimens of this beautiful little worm were ob- 

 tained, and the author was enabled to confirm the statements of 

 Grube and of Keferstein, who describe in it a double ventral 

 nerve chord, though other observers have failed to discover this 

 part of the neivous system and tlu'ow doubt upon its existence. 

 In adult specimens examined some years previously by the author 

 no ventral chord could be detected. 



The N'entral portion of the nervous system consists of two 

 flat ribbon-shaped chords which are given off from the in- 

 ferior side of the nerve ring which surrounds the pharynx 

 just behind the mouth. These run parallel to one another, 

 separated by a narrow interval ; they lie on the ventral walls 

 of the animal, and may be traced through the narrow tail- 

 like termination of the body as far as its extremity. They present 

 no ganglionic swellings, but opposite to every pair of feet each 

 sends off a filament which passes to the foot of its own side in 

 which it is distributed. 



Dr. Anton Dohm has just informed the author that he too had 

 distinctly seen the ventral chord of Tomopteris. 



SCIENTIFIC SERIALS 



Amongst the papers in the October and November numbers 

 of the American Aciluralist, are included Dr. J. L. Smith's 

 Address to the American Association for the Advancement of 

 Science, on Science in America and Modem Methods of Science. 

 — Mr. R. Ridgway describes some new forms of American 

 Birds, which he considers as geographical races, and not distinct 

 species. Included are Calherpes mc.yicanns, var. conspersus, ; 

 Hclminthophaga celaia, var. lutesccns ; Dcndroica vieiUotii, var. 

 luyanti ; D. domiiiica, var. albilora ; D. gracitc, var. decora ; 

 Myiodioctes pnsillus, var. pileolala (Pallas), and Colliirio ludovici- 

 aiiiis, var. rohustus (Baird), which are described and followed by 

 a synopsis of the genera of CtvV/i/i'A/, Jnnco, and Cardtnalis. — 

 Prof. C. A. Riley h.is a paper on the Oviposition of the Yucca 

 Moth, in which he shows that the female conveys her eggs into 

 the young fruit by a lateral puncture. The Structure and 

 Growth of Domesticated Animals, forms the subject of a popular 

 lecture by Prof. Agassiz, which is followed by one on Staurolite 



