ECTOPARASITIC TREMATODES. 265 



groups is only indicated by the presence of a notch in the 

 posterior border of the area occupied by the glands (fig. 1). 

 The apparently distinct borders observed and figured by the 

 preceding authors are caused by the presence of the numerous 

 outlets of the unicellular glands, which open close to each other 

 on the lateral portions of the ventral side of the membranous 

 j^ortion and are totally absent from the mediau groove separat- 

 ing them (fig. 2). These outlets contain, especially in their 

 terminal parts, more or less secretion of a granular appearance 

 having a great afiinity for stains, and thus impart a dark aspect 

 to the area occupied by them, whether in surface view or as a 

 transparent object, or whether stained or not. The cells them- 

 selves are goblet shaped, the necks are very long, and the cell 

 body is either finely or coarsely granular, or is filled with large 

 vacuoles, according to the stages of secretory activity. 



The posterior sucker is provided with three pairs of chitin- 

 ous hooks of the form shown in fig. 4, which represents those 

 of the right side as seen from the vental surface. The most 

 anterior piece is very stout and nearly straight and is sharply 

 pointed at both ends ; its length is 0.772 mm. The middle 

 piece is much more slender and strongly recurved ; it is very 

 long, being 1.38 mm. The posterior piece is exceedingly small 

 and consists of two portions, the basal flat portion somewhat like 

 the scales of Lepidoptera, and the distal hook like portion ; the 

 total length is only 0.099 mm. Besides these three pairs of 

 hooks there is, imbedded in the mesenchyma, usually a group 

 of chitinous granules of an irregular shape on the inner side of 

 the anterior piece. 



According to the statements of van Beneden and Hesse 

 ['64, p. 71] and of Cunningham ['90, p. 94] there are only two 



