SOME ROTIFERA FROM SPITSBERGEN. 329 



did not resume feeding but contracted into the position shown 

 (fig. 6 a) wherein the head and neck are retracted within the 

 central body. (The internal organs of the rotifer are omitted 

 or barely indicated, so that the position taken by the parasite 

 may be more clearly understood.) This position of the parasite 

 has been approximately identical on all four occasions. The 

 parasite is shown with its head resting upon or gripping in some 

 way the lower part of the stomach near its junction with the 

 intestine (see also fig. 6 b drawn from the second Spitsbergen 

 example). Behind the head of the parasite follows a long 

 tubular body, which passes nearly to the side of the rotifer and 

 then abruptly changing its course passes forward to the anterior 

 dorsal margin of the seventh segment of the rotifer (i.e. of the 

 first central segment), almost in the median line. Thus the 

 parasite has its posterior extremity well forward in the rotifer, 

 while its head is far to the rear. I was able to make out a ter- 

 minal and somewhat thickened segment (fig. 6 c). At the point 

 stated above, the skin of the rotifer seemed to be pushed upwards 

 and outwards in a gentle swelling (fig. 6 c). I had proof later that 

 at this point the parasite maintained its communication with 

 the exterior of the rotifer, and it is suggested that it is probably 

 also the point where the parasite had gained admission to its 

 victim's body, penetrating through the softer integument of 

 the invaginated skin between the sixth and seventh segments of 

 the body of the rotifer. So far as I could make out, the parasite 

 seemed by sucking with its head or mouth to be swallowing 

 fluid drawn from between the two membranes of the stomach wall 

 of the rotifer. At intervals of from 30 to 60 seconds, occasion- 

 ally even more, the long central body of the parasite gradually 

 distended and then suddenly collapsed, becoming only dis- 

 cernible with difficulty, but presently coming gradually into 

 view again as a long bladder apparently containing fluid only. 

 The collapse although nearly instantaneous in its action 

 throughout almost the whole length of the central portion 

 of the parasite was not quite so. I noticed that the 

 movement began near the head, and that the muscular impulse 

 involved, whatever be its exact nature, travelled from the head 

 backwards to near the posterior segment. While the tube was 

 being distended the portion immediately before the terminal 

 segment was apparently unaffected, but I succeeded in seeing 



