56 CEYLON PEARL OYSTER REPORT. 



Tetrarhynchus, sp. Cysts (/3). 



Two different kinds of cysts were found in a second specimen of Chirocentrus 

 dorab taken at Marichchukaddi. One closely resembled T. balistidis, the other was 

 enclosed in a cyst of peculiar form. The head of the animal lay in a little golden 

 cyst, 2 millims. long by 1 millim. broad, which is continued posteriorly into a long, 

 thin tail some 8 millims. or 9 millims. long. 



CYBIUM GUTTATUM, Guv. and VAL. 



This fish, one of the " Mackerels " or Scombridse, harboured two kinds of Tetra- 

 rhynchid cysts. The " Seer," as it is called, is one of the most esteemed food-fishes 

 of the Europeans in Ceylon. 



Tetrarhynchus, sp. Cysts. Plate III., figs. 42 and 43. 



A number of Tetrarhynchid larvae were taken from the peritoneum of a Cybium 

 guttatum captured off Trincomalee. Like those described in Part II. of this work 

 as T, balistidis, they exist in two stages, one in a cyst, the other without a cyst. 

 Whether one of these is, as we assumed in our description of T. balistidis, an older 

 form of the other, or whether they represent separate species, is uncertain. That 

 they are both larval is shown by the entire absence of any proglottides. The form 

 without the cyst is somewhat egg-shaped, 4 millims. long and at its widest 2 millims. 

 broad (Plate III., fig. 42). The most interesting feature in it is that the tail or 

 posterior end is ensheathed in a circular fold like a petticoat, and from it runs 

 up a number of ribs or ridges which fade out in the head. The teeth on the 

 proboscides are large and stout and comparatively sparse (Plate III., fig. 42). 



The other larvae, which on the whole we are inclined to regard as a different species, 

 are enclosed in a voluminous cyst which may attain a length of some 14 millims. 

 and a breadth of 2*5 millims. They were dissected out from the peritoneum of 

 C. guttatum. The larval head is very much smaller than that just described ; 

 it is invaginated, and the walls of the cavity in which it lies meet and all but fuse 

 (Plate III., fig. 43). They are then continued backward as the wall of the cyst, 

 which is constricted here and there. Posteriorly the exit of the excretory system 

 is visible. The cyst is enclosed in a secondary cyst pathologically formed from the 

 tissues of the host in which it lives. They evidently belong to the second group 

 into which VAULLEGEARD divides the Tetrarhynchidse, the type of which is 

 T. erinaceus. 



In another specimen of Cybium guttatum, taken at Marichchukaddi, there were 

 several cysts very like those described above, and two very different species of 



Trematode. 



DIAGRAMMA, sp. 



Tetrarhynchus, sp. Cysts. Plate III., fig. 44. 



A number of Tetrarhynchid cysts were taken from aii undetermined species of 

 Diagramma, a sea-perch common in the hotter parts of the Indian and the Pacific 



