1 :> ") 



Mr. W. Nicoll un Trcinalo>lc 



On inioroscdpic examination of a pressure preparation 

 (PI. IV. fig. 2), the sporocysts contained cercarisc varying in 

 nnml)er from two to as in.^ny as fifty, while the total number 

 of ccrearife sometimes exeeeded 250. Inside the sporoeyst 

 they appear of different shapes and sizes, hut on being pressed 

 out they assume an oval outline, elianging, however, with the 

 movements of the animal. 



These movements are interesting. Fully extended (text- 

 fig, a), the cercaria is spindle-shaped, and fixing itself in 



a 



Movements of cercaria. 



this position by its oral sucker it begins to draw the re- 

 mainder of the body up to the sucker. The anterior part 

 expands [b), the rest remaining narrow and elongated, but 

 this is gradually drawn forward until the whole body has the 

 sliape of a prolate spheroid {d). The ventral sucker then 

 comes into action, the oral is released and the anterior part 

 of the body begins to elongate until fiually the spindle- 

 shape is reassumed. 



The cercaria^ (PI. IV, fig. 3) vary in size, the average length 

 being about "22 mm. At the period of greatest contraction 

 the length may be '11 mm., -while at full extension it reaches 

 •28 mm. The greatest breadth is about '1 mm. 



The whole suii'ace of the cuticle, except on the suckers, 

 is set with small spines arranged in transverse rows, the 

 members of each row alternating with those in the next. Of 

 the two suckers the oral (PL IV. fig. 3, a.s ) is the larger; it is 

 subterminal and cup-shaped, with a circular aperture. The 

 ventral (tig. 3, v.s.) is just in front of the bifurcation of the 

 excretory system. The mouth opens in the oral sucker, and 

 viewed from the side it has a triangular outline. It is con- 

 tinuous with a pharynx (/*//.), the lumen of which has a 

 small dilatation at both ends. The oesophagus is short and 

 divides into two sac-like diverticula [div.). The excretory 

 system {ex.) occupies the major part of the body. In most 



