CESTODE AND NEMATODE PARASITES. 55 



There is practically no neck ; the sharp, unstained clear lines which represent the 

 division between one proglottis and the next begin close behind the head. At first 

 the proglottides are much broader than long, but they very soon become square and 

 then much longer than broad, till at the hind end the length is six or seven times 

 the breadth. There are only seventeen or eighteen proglottides in all. Unfor- 

 tunately the details of the inner anatomy refused to reveal themselves by staining. 

 Two peculiarities of the body are the way it is coiled up, as is characteristically 

 shown in Plate III., fig. 38, and the rapid rate at which the proboscides lengthen. 



Habitat: The intestine of ChiloscyWtum indicum. 



CHIROCENTRUS DORAP, (Forsk.). 



This fish, the only representative of the family to which it belongs, inhabits the 

 Indian Ocean and the seas of China and Japan. It is known as "Valai" or "Walai" 

 in Tamil, and as " Katuwalla," Sinhalese, literally a " bunch of thorns," a reference to 

 the multitude of needle-like bones that are present in this fish. Our specimen was 

 caught at Kalpitiya, Ceylon, on December 29, 1904, and contained Trematodes in the 

 anterior end of the intestine and Tetrarhynchid cysts. 



Tetrarhynchus, sp. Cysts (a). Plate III., figs. 40, 40a and 41. 



A number of small cysts containing Tetrarhynchus heads were found in the body of 

 Chirocentrus dorab, taken at Kalpitiya. They were all taken from the peritoneum. 



The cysts are 8 to 12 millims. long, and consist of an oval head 0'7 millim. in 

 breadth and 1 millim. in length, and a long flaccid tail about 0'3 millim. to 0'4 millim. 

 in width. The larval Tetrarhynchus lies entirely in the head (Plate III., figs. 40 and 

 41). It consists of a head and a small unsegmented body piece. The head shows 

 well the four proboscides with their teeth, the proboscis-tubes and the proboscis- 

 bulbs. 



The whole cyst is contained in an outer sheath, which is probably a portion of the 

 host. The Cestode part resembles a cysticercus which has been drawn out into a long 

 tail. The head of the Tetrarhynchus is invaginated into the sac, but the outer wall of 

 the invaginated portion seems to fuse with the inner wall (which is, of course, the 

 actual outer wall of the Tetrarhynchus head) near, but not quite at the posterior end. 



The whole cavity of the cyst, into which the end of the larva sticks, is full of cells 

 sparsely distributed with apparently many vacuoles containing fluid between the cells. 

 The nuclei are large. The same tissue occupies the lumen of the tail. 



Judging from the number collected, these cysts must have been common in the fish. 

 Unfortunately, it was impossible to make out any detail of the teeth in the retracted 

 proboscis, and as the head alone was present, all characteristics of the proglottides 

 were equally hidden. Hence nothing could be done to determine the species. 



