CTENOFHORES OF THE ATLANTIC COAST OF NORTH AMERICA 45 



at a lower level, the 2 paragastric and 2 tentacular vessels. All of these 

 canals are of slender caliber. 



The 4 interradial vessels {i, fig. 61, plate 12) fork near their aboral 

 ends, and give rise to 8 adradial vessels {ad, fig. 61, plate 12). The adra- 

 dial canals leading to the meridional subventral vessels are relatively 

 long, but those leading to the meridional subtentacular vessels are 

 very short. The subtentacular vessels, st, give rise to 4 short rows 

 of combs and also extend outward and downward (oral-ward) beyond 

 their points of origin, and then bend inward and finally outward along 

 the middle of the broad sides of the body and at last join with the 4 

 meridional subventral canals at the middle of the tips of the ribbon- 

 like body. The oral forks of the paragastric canals also fuse with the 

 meridional canals at this point, and in their course along the almost 

 knife-edged oral side of the body one finds numerous, simple tentacles. 

 The oral forks of one side of the body do not connect with those of the 

 opposite side, and there is no ring-canal around the mouth. There are 

 neither tentacles nor combs upon the narrow^ lateral ends of the body. 

 The 2 rudimentary, axial tentacles are each set within a deep sheath in 

 the side of the body close to the side of the paragastric canals. 



The sexual products are developed throughout the entire lengths 

 of the 4 meridional subventral canals under the combs of cilia. 



The young animal is transparent, but when old it often becomes 

 violet with a beautiful greenish-blue or ultra-marine fluorescence (see 

 Chun, 1880, Ctenophoren des Golfes von Neapel, p. 152). 



The embryonic development has been well described by Chtin, 

 1880, pp. 135-141. The larva passes through a Mertensia-like stage 

 wherein the tentacular diameter is longer than the stomodaeal axis, al- 

 though as growth proceeds the stomodaeal axis becomes so enormously 

 extended that the body is reduced to the shape of a flat ribbon. While 

 in the Mertensia stage there are about 4 ciliated plates on each of the 

 meridional subventral and i ciHated plate on each meridional subten- 

 tacular canal. The meridional canals and the paragastric canals at first 

 end blindly, but their free ends extend outward and downward and finally 

 fuse with the oral forks of the paragastric vessels. The larva is strik- 

 ingly like the Cydippidae and shows the evident derivation of Cesium 

 from this order, but the general plan of the canal-system resembles that 

 of the immature Beroidas, in the separation of the peripheral canal sys- 

 tems of the two sides of the body although in the mature Beroidae a 

 circum-oral canal develops in some species, and all of the meridional 

 vessels become connected by a network of fused lateral branches. 



Cestum veneris is abimdant in the Mediterranean and is also found 

 in the tropical Atlantic. At Tortugas, Florida, it is not often met with, 

 but can not be called rare. The so-called Cestum amphitrites Mertens, 

 of the tropical Pacific, appears to be identical with the Atlantic and 

 Mediterranean C. veneris, and Bigelow, 1904, appears to have described 

 this form from the Maldive Islands, Indian Ocean, under the name 

 Cestum pectenalis. Wagner, 1885, records the capture of Cestum veneris 

 in the White Sea and this is the most northerly locality from which this 

 Ctenophore has been reported. It was probably swept northward along 

 the Norwegian coast in the Gulf Stream drift. 



