I9I5-] 



Fauna of the Chilka Lake : Coelenterates. 



8 7 



There are two pedicellate groups, alternating with the single tentacle, above 

 each complete intermesenterial space ; each group is associated with one com- 

 plete and three incomplete mesenteries and its lumen is continuous with that of 

 three incompletely separated compart- 

 ments; one of its internal walls is 

 practically co-terminous with a com- 

 plete and the other with an incomplete 

 mesentery, while the upper extremi- 

 ties of two other incomplete mesen- 

 teries are continued into it. The 

 pedicel itself is a hollow process of the 

 margin of the oral disk ; its length is 

 considerably greater than its breadth ; 

 it is compressed from above down- 

 wards ; it has parallel sides. At some 

 little distance from its point of origin FlG - S—Pelocoäes exul (Annandale). 



the process bifurcates in a horizontal Transverse section of the column in the muscular 

 plane and just within the fork a single region ' from a hi § hly contracted specimen. 

 tentacle, which we may call the furcal tentacle, arises on the upper surface. Each 

 branch of the pedicel bears two, three or four tentacles; the number is variable, 

 sometimes even on the disk of a single individual. 



In the lower or posterior wall of the pedicel there are, projecting into its lumen, 

 four muscular ridges, two practically at the lateral margins and two in the middle. 

 These ridges are actual prolongations upwards and outwards of the four mesenteries 

 with which this process is associated ; above and opposite each of them on the upper 

 or anterior wall a similar ridge is developed, so that the whole lumen is divided in- 

 completely into three chambers, the two outer pairs of ridges being close to the sides 

 of the pedicel. The separation is incomplete because the united depth of the two 

 ridges of each pair is not so great as that of the lumen. The furcal tentacle is pro- 

 duced at the distal extermity of the central chamber, while each of the lateral cham- 

 bers corresponds to one branch of the pedicel. The number of tentacles developed 

 on each branch is evidently a matter of secondary importance. 



Although one of the lower ridges in each pedicel is connected with a complete 

 mesentery while three are continuations of incomplete mesenteries, no difference in 

 structure can be observed ; nor is there any difference between these lower ridges 

 and the corresponding upper ones. 



The walls of the pedicel and of the tentacles are very thin, the mesogloea and 

 the circular muscles being poorly developed in them. The longitudinal muscles, 

 though by no means thick are, in spite of the non-retractile and not highly contrac- 

 tile state of the disk, well developed. The mesenteries closely resemble those of 

 Phytocoetes, except that there are 36 instead of 12 incomplete mesenteries and 

 that the filaments are more uniformly developed on the complete ones. 



In the case of Phytocoetes the difference between the microscopic appearance of the 



