297 



examination, it would be quite pardonable if an observer were to come 

 to the conclusion that be had to do with a Monocystis or allied Grega- 

 rinid. The use of liigh powers however shewed unmistakeably (1) that 

 there is a mouth and gullet (2), that there is a stigma (3) that there is a 

 contractile vacuole and reservoir. Furthermore in some specimens a 

 rhythmical movement could be detected within the gullet. 



Specimens freed from the host sooner or later undergo a change. 

 Within two hours in some cases, but often only after the lapse of a con- 

 siderably longer time, the euglenoid movements cease, and are succeeded 

 hy much more active spinning and rolling movements , which are found 

 to be brought about by the agency of a flagellum. Often they retain a 

 bottle-like shape for a considerable time after the ai^pearance of the 

 flagellum, and revolve rapidly round the long axis. Eventually they 

 assume the form which is characteristic of the Euglena e in general 

 when they are not undergoing " euglenoid '" movements. The flagellum 

 is about half the length of the body, and its movements are rapid-about 

 ten to a second. Chromatoi^hores were not developed, though freed 

 specimens were kept alive for several days. 



In the case of the Euglena-like form which I had previously obser- 

 ved (and which may be identical with the one now under consideration 

 though found in a different host) the parasites were to be seen moving 

 about within the protoplasm of certain of the cells of their hosts, often 

 pushing aside the nucleus, or displacing protoplasmic filaments. The 

 form occurring in the Mesostomid is not so easily to be observed in situ 

 in the living condition, owing to the thickness and opacity of its host. 

 It was seen, however, to be abundant among the spermatozoa in the 

 vasa deferentia and vesicula seminalis. In sections it was found to occur 

 within the cells of the digestive epithelium: but to be most numerous in 

 the spaces between the gut and the body-wall. No free Euglenae 

 were found in the water in which the Turbellarian hosts were living. 



It is somewhat remarkable that this peculiar kind of parasitism has 

 escaped notice. In his recently published momoir »Die Turbellarien als 

 Parasiten und Wirte« Graff's only reference to flagellate organisms as 

 parasites of Turbellaria is as follows: — » Flagellât en-ähnliche Organis- 

 men mit lebhaft schwingenden Geißeln sind bisher bloß in den Neben- 

 taschen der Bursa seminalis von Monocelis fusca Orst. gefunden wor- 

 den« (p. 59). 



20 



