﻿32 MUSGRAVB. 



were quite large, averaging 0.015—0.018 in length, whereas those taken 

 from the lung in the same case weje only 0.010-0.015. The worms eon- 

 tract under the influence of all preservatives, and measurements made 

 with specimens which have heen subjected to this influence give still 

 more uncertain results. 



Color: The color, when the trematode is first removed from the ani- 

 mal host, varies from a dark reddish-brown to a light slate. After it has 

 been exposed to the air for a short time, the surface takes on a dull- 

 grayish appearance, similar to that seen in the preserved specimens. 



Shape: When the parasite is alive its shape is somewhat variable, but 

 on the whole it is fairly constant; it is oval, the more acute pole being 

 the caudal extremity. The ventral surface is more flattened than the 

 dorsal one and at times it is even concave, except at the extreme cephalic 

 end, where the ■ more spherical shape is maintained. Specimens are 

 always altered while in preparation; this is probably due to the more 

 rapid absorption of the chemicals by certain portions of the body and 

 the consequent uneven contraction. 



Motility: There does not appear to be much in the literature concern- 

 ing the motility of these worms. The parasites do not appear to have 

 more than a slight power of active locomotion when they are removed 

 from the host, but motions of different portions of the body may be seen. 

 The most interesting of these gives the trematode the ability to pro- 

 trude and retract its head by stretching or contracting that part of the 

 body cephalad of the acetabulum, and again it has the power of altering 

 the plane of the oral sucker in a like manner, so that at times the latter 

 may appear to be directly terminal and again almost completely sub- 

 terminal. These two motions may be observed in a much more striking 

 degree in members of the genus O pistil orchis. 



Cuticle: A rather thick, dense skin envelopes the entire parasite, but 

 when it is carefully studied in serial sections cut longitudinally and trans- 

 versely (see Plates Y, VI, VII, and VIII) it is seen that this cuticle is 

 not of equal thickness throughout, it being heavier on the dorsal and lat- 

 eral surfaces than it is on the ventral one. Even in some places on the 

 dorsum it is thicker than it is in others. M, the cephalic end, the struc- 

 ture of the cuticle is more closely interwoven with that of the deeper 

 tissues. 



Spines: Almost the entire body of this worm is covered with scale-like 

 spines, which are of different sizes in different locations, and in certain 

 places, such as the ventral surface from the acetabulum to the oral sucker, 

 they are almost entirely absent. The spines in this situation, wherever 

 they occur, are smaller than the others; they gradually increase in size 

 on the lateral borders and they reach a maximum on the dorsum. This 

 seems to be true whatever transverse plane of the body is studied, but it 

 is particularly marked about the region of the acetabulum. Again, in 



