1904.] ON A KECENTLY DISCOVEEED TURBELLARIAN WORM. .407 



2. On the Turbellarian Worm Avagina incola, with a Note 

 on the Classification of the Proporldoe. By Robert 

 T. Leiper, Research Student, Glasgow University 

 (Embryological Laboratory)*. 



[Received February 2, 1904.J 

 (Plate XXY.)t 



The Turbellarian which forms the subject of the present paper 

 was briefly described by me at the Meeting of the British Associa- 

 tion for the Advancement of Science held at Belfast in 1902. 

 The chief characters were pointed out and the name of Avagina 

 incola gen. et sp. nov. given to it, in a report of that Meeting in 

 'Nature' (c/. vol. Ixvi. p. 641, 1902). 



It was observed by me to be present in the " accessory canal " 

 of about five per cent, of the specimens of the common Heart- 

 Urchin, Echinocardium co7-datum Penn., collected fi'om Kames 

 Bay, Cumbrae, N.B., in the summer of 1902, and is of interest as 

 being the only recorded example of distinct parasitism among the 

 Acoelous Turbellaria (m.) +. 



General Features (Plate XX Y. figs. 1, 2). 



A. hicola is whitish and moderately translucent in appearance, 

 leaf -like in shape, obovate in outline when contracted, lanceolate 

 when extended, the blunt end being anterior. It measures in 

 length 2"5 mm., in breadth transversely "G mm., dorsi-ventrally 

 •2 mm., and progresses by a slow creeping spiral movement. 

 Sevei"al examples are usually found in the same host. 



Integument (Plate XXV. fig. 3). 



The integument consists, as in other Acoela, of (1) a muscular 

 network of single, circular, oblique, and longitudinal fibres abutting 

 on the superficial parenchyma, and (2) a granular cuticle unifoi-mly 

 covered with cilia. Not unfrequently along the ventral surface, 

 but seldom on the dorsum, the cuticle is swollen by vesicular 

 structures which are sometimes surmounted by large granular - 

 projections (fig. 3, A, B). There are no rhabdites or sagittocysts. 



Mouth (Plate XXY. fig. 4). 



The mouth is merely an opening in the cuticle exposing the 

 superficial parenchym. Its position on the under surface at about 

 the junction of the anterior fourth with the rest of the body is 

 recognisable in the living animal, even from the dorsal surface on 

 careful focussing, by the converging action of the cilia. There is 

 practically no pharynx. 



* Communicated by the Secketart. 

 t For explanation of the Plate, see p. 411. 



X Roman numerals in brackets refer to the List of Literature given at the end of 

 this paper. 



