A. Porter 
0i>0 
gland (or “liver”) of the mollusc being infected. Other limpets were 
examined for herpetomonads, about fifty in all, and eight per cent, of 
the total examined were found to be slightly infected. The range 
of the genus Herpetomonas is thus extended to the Mollusca, and the 
digestive gland is added to the organs of a host that may harbour 
such parasites. The name Herpetomonas patellae is proposed for this 
new flagellate. 
I have much pleasure in thanking Professor Herdman and Mr H. C. 
Chadwick for their kindness in facilitating my researches at Port Erin, 
Isle of Man, in Nov. 1913, when the parasite was found. Mr Chadwick 
greatly aided me in obtaining material. Observations were continued 
near Brighton in May 1914. Preparations were further studied and 
the research was completed in Cambridge in the laboratory of Professor 
Nuttall, to whom my thanks are due. 
Observations on living Herpetomonas patellae. 
The flagellate herpetomonads appear as very small, somewhat 
retractile organisms and move jerkily, the body being sharply flexed 
and then straightened and the flagellum lashing vigorously. Swirling 
movements, suggestive of those of a boomerang, are common. The 
flagellum is thick and is easily seen in life. It is often as long as the 
body. The flagellar end is forwardly directed in movement. The 
parasites showed no tendency to collect in groups and neither division 
rosettes nor aggregations \vere observed. A few dividing forms were 
watched and multiplication by simple longitudinal fission was the 
only mode of increase seen. A few young flagellates were found in 
the stomach of the limpet; full grown forms were most abundant in 
the “liver.” A few were observed in the rectum and faeces. 
The part of the “liver” adjacent to the stomach also contained 
ovoid, non-flagellate forms of the parasite. Some of these in a fresh 
preparation were watched for several hours, and the gradual production 
of a flagellum with subsequent elongation of the body was seen in 
individual cases. The flagellum was often formed before the distal 
or posterior end of the body lengthened. A few thicker walled post- 
flagellate forms were found in the distal end of the “ liver,” as well as 
in the rectum. 
Morphology. 
The morphology was studied both in the living organism and in 
stained preparations. Smears of the gut contents and of the digestive 
