4 CTENOPHORES OF THE ATLANTIC COAST OF NORTH AMERICA 



ciliary combs beneath and along the line of which there extends a meri- 

 dional longitudinal vessel. 



Two other vessels, the paragastric canals, arise from the funnel- 

 cavity in the tentacular plane and extend downward close to and along 

 the middle of the broad sides of the stomodaeum. 



As this canal-system is complex I have sought to make its arrange- 

 ment clear by presenting a diagram in figure i, which should be con- 

 sidered seriously only in so far as it is diagrammatic, and should be 

 compared with figs. 4 and 5, which illustrate the conditions seen in 

 Pleurobrachia pileus. This diagram attempts to show a perspective view 

 of the gastro-vascular cavity. The mouth, m, leads into the laterally 

 flattened, slit-like cavity of the stomodaeum, st; this in turn leads into 

 the laterally flattened infundibulum or funnel, /, the flat side of which is 

 90° apart from the flat side of the stomodaeum. The axial fvmnel-tube, ft, 

 leads upward from the funnel to open to the outside through the excre- 

 tory pores, ex. The long, narrow ridge of the pole-plate, p, lies in the same 

 plane as the stomodaeum and 90° apart from the axis through the funnel 

 and tentacles. The funnel, /, gives rise to two tentacular canals, t, two 

 paragastric canals, g, and four interradial canals, i. The four interradial 

 canals bifurcate and give rise to eight adradial branches, ad, which lead 

 to the meridional canals, which are not shown in this figure, but which 

 extend along under the combs of cilia. 



In the Cydippidae the eight meridional canals and the two paragas- 

 tric vessels end blindly near the oral end of the body, but in the higher 

 ctenophores of the orders Ganeshidae, Lobatae, Cestidae, and Beroidae their 

 oral ends fuse in various ways, forming more or less complete circuits. 

 Stages in the development of these fusions are shown in fig. 39, plate 6, 

 and figs. 16 and 18, plate 5, and the completed circuits are clearly shown 

 in fig. 56, plate 10, which illustrates the condition in Ocyropsis wherein 

 there are neither tentacles nor tentacular canals to complicate the figure. 



Figure 2 is a diagram intended to make clear the plan of these fusions 

 between the meridional and paragastric canals in the Lobatae. For the 

 sake of clarity I have left out the auricles, which are four ribbon-like 

 expansions of the body on the tentacular sides of the mouth, and around 

 the narrow edge of each of which the meridional, subtentacular vessels 

 extend. The tentacles and tentacular canals are also omitted in this 

 diagram. Vessels on the opposite side of the animal are dotted. The 

 diagram shows how the two paragastric canals, g, fork at their oral ends 

 and form a ring-canal surrounding the mouth,m, and the four meridional 

 subtentacular canals fuse with this ring-canal. The four meridional sub- 

 ventral canals, msv, which extend along the outer sides of the oral lobes 

 fuse in pairs to form two loop circuits in the lobes, one loop in each lobe. 

 This diagram applies only to the Lobatae. 



In the Cestidae, on the other hand, the oral forks of the paragastric 

 canal of each side of the body unite with the two subtentacular and 

 sub ventral meridional vessels of that side only. Thus in this order there 

 is no ring-canal around the mouth. This statement applies also to the 

 young of the Beroidae, although later the meridional vessels of both sides 

 become connected by anastomosing side branches which appear quite 



