498 University of California Puhlications in Zoology [Vol. 18 



the oral sucker is very clearly defined in a living cercaria or toto 

 mount. Under certain conditions this line appears as a constriction 

 which separates the so called "head" of the cercaria from the body 

 proper. 



The center of the oral sucker contains a large reservoir-like gland 

 (fig. 1, 2, hg) which opens almost exactly in the middle of the anterior 

 tip. This is called the "head-gland" by Miyagawa (1916, p. 67). As 

 noted by Miyagawa it is more coarsely granular than the cephalic 

 glands which fill the posterior half of the body. I will include a trans- 

 lation of the discussion in Miyagawa 's paper (1916, p. 67) in regard 

 to this gland: 



Head-gland = Kopf druse (of Narabayashi). 

 This gland occupies about half of the head at the dorsal part of the center. 

 It contains coarse granular material and is stretched or compressed with the 

 movements of the cercaria. It opens at the anterior end of the oral sucker. 

 This sac-like gland has been confused by many investigators with the buccal 

 cavity. In larvae examined after entering the skin it was found to be pressed 

 to one side and later disappeared. 



Since the head-gland degenerates soon after the cercaria has pene- 

 trated through the skin of its final host, IMiyagawa considered that it 

 is an adaptive larval structure which has some function connected 

 with penetration. Its position would also seem to support this view. 

 A layer of large nuclei surround the gland and are evidently a part 

 of it. The contrast between the head-gland and the cephalic glands 

 (figs. 1, 2, eg) is shown very clearly by reactions of their glandular 

 substances to stains. The head-gland in the sections studied took the 

 red stain (erythrosin), while the cephalic glands were stained a light 

 blue with haematoxjdin. 



The remainder of the oral sucker is filled with parenchymatous 

 tissue and the anterior portions of the ducts of the cephalic glands 

 (figs. 1, 2, dcg). The consistency of the oral sucker ivS such that its 

 shape can be greatly distorted by contraction of its muscles. The 

 ducts from the cephalic glands (figs. 1, 2. dcg) pass into the oral sucker 

 on each side near its ventral surface. They pass directly through the 

 muscular boundary of the sucker and run forward along each side to 

 open at the anterior tip of the cercaria. Near the openings of these 

 ducts at the anterior tip are located on each side four or five, forward 

 pointing spines (figs. 1, 2, as). The relations of the different parts 

 included in the oral sucker are shown clearly in figures 1 and 2. The 

 oral sucker is not radially symmetrical as is usually the case, but has 



