CTENOPHORES OF THE ATLANTIC COAST OF NORTH AMERICA 47 



terranean, and it is evidently distributed entirely across the tropical 

 Atlantic, being fairly common at times at Tortugas, Florida. 



The animal moves by vermiform contractions, aided by its combs 

 of cilia, and advances with remarkable rapidity by a series of sudden 

 darts with intervals of rest between. I have seen a perfect specimen of 

 this ctenophore which was swimming normally in an aquarium suddenly 

 tear itself into shreds through muscular contraction. 



Order BEROIDiE Eschscholtz, 1829. 



BeroidcB, Eschscholtz, 1829, Syst. der Acal., p. 35. — Gegenbaur, 1856, Archiv 

 fiir Naturgesch., Jahrg. 22, p. 192. — Agassiz, A., 1865, North Amer. Acal., 

 p. 35. — Chun, 1880, Ctenophoren des Golfes von Neapel, p. 303. — Moser, 

 1903, Ctenophoren der Si6oga-Exped., p. 19. — Vanhoffen, 1906, Nordisches 

 Plankton, Ctenophoren, p. 7. — Romer, 1903, Fauna Arctica, Ctenophoren, 

 Bd. 3, p. 81. — Benham, 1907, Trans. New Zealand Institute, vol. 39, p. 139. 



Agassiz regarded the Beroidae as the simplest of the ctenophorae 

 and considered that the more complexly organized Lobatae, Cydippidae, 

 and Cestidae were derived from them. They are simple in that they lack 

 tentacles and tentacular canals. The structure of the apical sense- 

 organ and the papillae of the pole-plate are, however, more complex than 

 in other orders of ctenophoras. Chun, 1880 (pp. 267, 271), contrary to 

 Agassiz, regards the Beroidae as the most highly differentiated of cteno- 

 phorae and considers that they have remotely descended from tentac- 

 ulate forms, and that they can not be regarded as the ancestral type from 

 which the existing tentaculate ctenophorae have been derived. 



The loss of the tentacles in the Berodiae may have come about, 

 according to Chun, through the powerful development of the cilia, giving 

 freedom and rapidity of motion, and through the great development of 

 the wide-flaring mouth which enables the animal to obtain food without 

 depending upon tentacles to capture prey. It is remarkable, however, 

 that no trace of tentacles or tentacular vessels appears in the larvae of 

 Beroidae, but we must remember that in the genus Ocyropsis of the 

 Lobatae there are neither tentacles nor tentacular vessels, so that the case 

 of the Beroidae does not stand alone and need give us no great concern. 

 Moreover, in essential respects the fusions between the oral branches of 

 the paragastric and the meridional canals are similar in Cestidae and 

 Beroidae excepting that in the Beroidae an anastomosing network may 

 connect some or all of the meridional canals one with another. 



The lateral diverticula of the meridional and oral branches of the 

 paragastric canals, which are seen only in the Beroidae, are evidently, 

 phylogenetically speaking, of recent origin, for they appear very late in 

 ontogeny in Beroe. 



It is probable that the Beroidae and Cestidae are derived from a com- 

 mon stock whose relationship to the Lobatae was close. 



The lateral compression in the funnel-axis is more marked in the 

 Beroidae than in any other order of ctenophores excepting the Cestidae. 



There are 2 genera, Beroe in which the aboral pole of the animal is 

 dome-like and oval, and Neis Lesson, in which there are 2 prominent 

 lobes on both sides of the apical sense-organ. (See von Lendenfeld, 

 1885, Zeit. fiir wissen. Zool., Bd. 41, p. 673.) 



