6 CTENOPHORES OF THE ATLANTIC COAST OF NORTH AMERICA 



lobe. There are numerous, simple tentacles which extend along the 

 wide sides of the mouth, and in the middle of each line there is usually 

 a principal tentacle, which is commonly feathered and arises from a large 

 projecting basal-bulb without a sheath. In Ocyropsis, however, there are 

 neither tentacles nor tentacular canals. The subventral rows of combs are 

 longer than the subtentacular. The larvae pass through a stage in which 

 they resemble the Cydippidas, from which the Lobatse are evidently 

 descended. In the larva the tentacular axis is wider than the stomodaeal 

 axis, as in Cydippidae, whereas the reverse is the case in the adtdt Lobatae. 



IV. Cestid^ : The lateral compression seen in the Lobatag is greatly accentuated 



in this order, so that the body is flat and ribbon-like, the long side being 

 in the stomodeeal axis and the compression being in the funnel-axis. 

 There is no ring-canal around the mouth, but the subventral and sub- 

 tentacular vessels unite with the oral forks of the paragastric canals 

 and the canal-systems of the two sides are separated, uniting only at the 

 funnel. There is a row of tentacles along the oral forks of the paragastric 

 vessels. The 2 median tentacles are the largest and are set within basal 

 sheaths. The Cestidas are closely related to Lobatae, and their larvae pass 

 through a cydippe-stage as do the larvae of the Lobatas. 



V. Beroid^ : Lateral compression as in the Lobatae and Cestidae, the compression 



of the funnel-axis being generally more marked than in the Lobatse, but not 

 so pronounced as in the Cestidas. Canal-system as in the Cestidae, with the 

 added feature that the meridional canals and the oral forks of the para- 

 gastric canals give off side branches which ma}'^ anastomose and form 

 a network connecting some or all of the vessels, in some species forming 

 a circumoral canal-system. The axial funnel-canal is absent and is replaced 

 by two side branches which extend upward from the funnel to the excretory 

 pores. There are no tentacles even in the larva, which in other respects 

 resembles the Cydippidae. The stomodsum is very wide in the sagittal 

 plane and constitutes a great sac, so that the funnel is very short. 

 VI. Platyctenid^ : Creeping or sessile, degenerate ctenophores, with the oral- 

 aboral axis much shortened, so that the oral and aboral sides of the 

 animal are fiat and expanded. With 2 tentacles, which in some forms 

 may be withdrawn within sheaths. The apical sense-organ may be present, 

 but in some forms the combs of cilia are absent. There are 3 genera, 

 Tjalfiella Mortensen, Coeloplana Kowalevsky and Ctenoplana Korotneff. 

 The species occur in the Red Sea, Malay Region, Japan, and Greenland, 

 and the most recent descriptions are by Willey, 1897, Quarterly Journal 

 Microscop. Sci., vol. 39, p. 323 ; Abbott, 1902, Annot. Zool. Japonensis, vol. 

 4, p. 103; and Mortensen, 19 10, Vid. Meddel. Foren. Kobenhavn, p. 249. 



In the extreme tenuity of their bodily substance and their diaphan- 

 ous delicacy of coloration, the ctenophores stand apart from other marine 

 animals. Their presence in the water is commonly denoted only by the 

 brilliant flash of rainbow colors which play along the lines of their cil- 

 iary combs as they move languidly beneath the unrippled surface of 

 the sea. Yet these creatures are no more wonderful in their complex 

 organization than in their remarkable adjustment to their habitat, for 

 so delicate are most of them that a current such as that of an oar suffices 

 to tear them into misshapen shreds — a fate which they escape in time of 

 storm by sinking far into the depths. This fact accounts for the extreme 

 rarity of many of these forms, for the ocean's surface must have remained 

 flat as a mirror for many hours before they can be lured upward from the 

 calm of their deep retreat. Yet tender as they are to the touch, passing 

 jelly-like between the fingers of the hand that attempts to seize them, 

 their food consists largely of young fishes which they engulf in great 

 ntunbers, seizing their prey by means of their peculiar " Greifzellen " (see 

 Chun, 1880, Ctenophoren des Golfes von Neapel, p. 225, Taf. 18). Thus 

 in the cold northern waters where ctenophores occur in vast swarms, 



