ON TETRACOTYLE PETROMYZONTIS. 489 



On Tetracotyle petromyzontis, a Parasite of 

 the Brain of Ammocoetes. 



By 



Albert \V. Bio\\T«, B.A., F.L,.S., 

 Formerly Exhibitioner of Christ Cliurch, Oxford. 



With Plate 39. 



Whilst I was working as a student in the Department of 

 Comparative Anatomy at Oxford, in the Histology Class of 

 Mr. G. C. Bourne, my attention was drawn to a very extra- 

 ordinary appearance in some sections of the brain of Ammo- 

 coetes. Examination of sections of several different individuals 

 revealed a constancy in the appearance at first sight suggestive 

 of some highly complex abnormality, but a more thorough 

 examination of series of sections resulted in the discovery that 

 I had to deal with a parasitic form, which eventually proved 

 to be a Holostomid trematode. 



Now the occurrence of a Trematode in the brain cavities of 

 a vertebrate is a unique phenomenon, occurring, so far as I can 

 discover, in no other case, and it therefore seems desirable to 

 publish some sketches and a description of the structure of 



the parasite. 



At the outset I wish to tender my thanks to Mr. G. C. 

 Bourne for his help during the early stages of the work. My 

 best thanks are also due, and cordially given, to Professor 

 Bay Lankester, in the stimulating atmosphere of whose 

 laboratory the work was done. Professor W. B. Beuham, 

 recently lost to Oxford, gave me much assistance throughout 

 my work, and I am especially grateful to him for drawing my 



