492 ALBERT W. BROWN. 



appearance when the parasite is present in large numbers. 

 I have kept several Aramocoetes alive for nearly three months, 

 during which time they have lived and grown quite normally. 

 On killing and opening, the brain was found packed full of 

 parasites. 



Tetracotyle petromyzontis will live for some time 

 outside the brain ; Gulliver says for several days, but mine 

 have never lasted more than three hours. Whilst alive they 

 fix themselves by the ventral sucker, and, contracting rhyth- 

 mically, undergo rapid changes of shape. Outline sketches to 

 illustrate these changes are seen on PI. 39, fig. 2. 



External Characters. — Tetracotyle petromyzontis 

 has an average length of about '42 mm. It possesses atypical 

 fluke-like form. At the posterior end of the body, which is 

 slightly broader than the anterior, the rudiments of the tail, 

 in which the adult generative organs are developed, are visible. 

 The mouth is at the anterior end, and is surrounded by the 

 oral sucker. On each side of it are two retractile ear-shaped 

 projections with which numerous gland-cells are connected. 

 About midway on the ventral surface is situated the ventral 

 sucker, and just posterior to this the large glandular adhesive 

 organ. At the posterior end of the body is the excretory 

 pore. 



The intestine, which is easily seen under a low power of the 

 microscope, is Trematode in character. Some little distance 

 behind the mouth it expands into a powerful pharynx which 

 seems to perform a kind of pumping action during life. 

 Behind the pharynx the intestine forks, each fork ending 

 blindly just posterior to the glandular adhesive organ. 



The body appears filled with a number of bright globular 

 bodies. These are contained in the terminal vesicles of the 

 excretory system. 



Careful focussing shows the integument dotted all over the 

 surface with minute black dots arranged in regular rows. 

 Sections prove these to be minute canals piercing the cuticular 

 layer (PI. 39, tig. 3). 



Internal Anatomy. — Below the ectoderm come the usual 



