ON A LARVAL CESTODE FROM THE UMBRELLA OF A JELLY-FISH. 



By T. Southwell. 



Dr. Annandale, Director of the Zoological Survey of India, has been kind enough 

 to place at my disposal a number of parasites obtained from the umbrella of a Rhi- 

 zostomous medusa (Acromitus rabanchaUi) collected from near Barkuda Island in Lake 

 Chilka on August 21st, 1920. 



I had previously seen these parasites during inspections made of the fish fauna 

 in the Chilka Lake, but no opportunity occurred of examining them carefully. The 

 material was contained in three phials, preserved respectively in corrosive acetic, 

 formalin and absolute alcohol. All the material was in excellent condition, that 

 preserved in corrosive acetic being by far the best, and that preserved in absolute 

 alcohol the least satisfactory of the three. 



Technique. — Seven specimens were stained for two days in very dilute acetic- 

 alum-carmine. Four of these were mounted whole, two were serially sectioned 

 transversely, and one serially sectioned longitudinally. 



Two unstained specimens were sectioned as above and afterwards stained with 

 haematoxylin and eosin. Two unstained specimens were mounted whole. 



Structural Details. — The larvae are cylindrical, with broad rounded extremities, and 

 they measure from 2 mm. to 2.5 mm. long; the diameter is 340 M (figs, a and b). 

 They lie in cavities in the host, but are not surrounded by a definite adventitious cyst, 

 although there is a slightly marked condensation of host-tissue round them. 



Both fresh and preserved specimens have a milky-white colour and can be seen 

 easily with the naked eye, especially in the fresh condition. The larva is solid and 

 is covered with a definite cuticle. There is a very definite sub-cuticular tissue made 

 up of a series of small spindle-shaped cells, closely packed together, the nuclei of 

 which stain deeply (fig. c). Internally the larva consists of a stroma framework, 

 enclosing a few large cells which in cross section measure about 38^ by 25 ,a. Their 

 anter o-poster.' or length was not determined. 



These cells are at first granular, but, later on, calcareous corpuscles develop 

 within them and gradually fill the cell. Eventually the calcareous corpuscles (which 

 are very large and numerous) become free, and the cells which secreted them are no 

 longer visible, being replaced by others apparently from the sub-cuticular layer. 



The anterior extremity is marked by a deep pit, lined with extremely small 

 spinules. The base of this pit is thickened, the thickened area consisting of very 

 numerous small elongated cells with well defined nuclei. As in other Cestoda the 

 head develops from the base of this pit. In our specimens development had not 

 proceeded beyond the formation of this pit and no trace of the head was to be seen. 



