46 WRIGHT AND MACALLUM. [Vol. I. 



pose to return to this subject after we have obtained more 

 definite information as to this point. 



Zeller has pointed out that the rounder and smaller Polysto- 

 mum eggs bear a short hook-like process at the hinder end. A 

 similar process is to be frequently seen on the hinder, more 

 pointed ends of the eggs in Sphyranura. These are probably 

 to be interpreted as persistent rudiments of the polar threads 

 so common in other monogenetic Trematodes. 



Explanation of Plate. 



Minute histological details are represented as seen with Leitz's ^^ inch 

 oil-immersion, although the same enlargement, as will be seen from the 

 figures, has rarely been retained. 



Fig. I. — Sphyranura, from ventral surface; X 35 ; m, 

 mouth ; pp, prepharnyx ; mp, muscular pharynx ; Ig, area of 

 lateral ganglion ; aiy anterior arch of intestine ; ga, aperture 

 of genital sinus ; cb, contractile bladder of water-vascular sys- 

 tem ; be, bulbus ejaculatorius ; u, uterus with a mature &g% ; 

 rs, one of the receptacula seminis ; <?z/, ovary; *, point of 

 entrance of overflow-tube into intestine ; vi, vitellogen. [The 

 ducts from the female sexual organs may be seen to converge 

 to a central ootype.] ; t, testicular lobules ; //, the posterior 

 arch of the intestine. 



Fig. 2. — Portion of investing membrane, with tactile organs 

 fresh ; X 300. 



Fig. 3. — Section through centre of caudal sucker, from a 

 sagittal series stained with iodine-green ; c, c* , the cuticularized 

 limiting layers of the sucker; tn, the muscle of the central 

 hooklet; X 155. 



Fig. 4. — Caudal lamina from ventral surface, showing the 

 form of the hooks and the position of the booklets ; a, b, c, the 

 muscles of the large hooks ; at d, some of the muscles of the 

 suckers; x 100. 



Fig. 5. — Hooklets and eyelets; x 550- 



Fig. 6. — From a horizontal series prepared with Flemming's 

 fluid and alum-cochineal. The section is in the plane of the 

 suprapharyngeal commissure, sc, and the dorsal wall of the 



