898 J- Staffoed, 



sucker but in No. 4 the proportion of mouth-sucker to ventral sucker 

 is as 5 : 4. The relative sizes of the suckers is not a very useful 

 distiug'uishing feature, since in four out of the five species there is 

 little diflference in this respect, and, besides, the ventral sucker is 

 difficult to See in adult worms, being obscured by the dark-coloured 

 Uterus. Its position is a little more than one-third the lengih of the 

 animal from the anterior end along the mid-ventral line. 



Cuticle. This in No. 1 is thick and perfectly smooth but in 

 all the rest it contains numerous backwardly projecting, sharp spines. 

 In the living worm, it must be studied as soon as the worm is 

 removed from its natural medium, for the cuticle soon disintegrates, 

 in contact with water or pressure. Killing fluids containing acids 

 are likely to destro}' both cuticle and spines so that niounted 

 specimens, whose history is forgotten, are not to be depended upon. 

 Worms killed in alcohol preserve these structures and should be 

 mounted as control specimens. 



The Muscular. Parenchymatous, Digestive, Glan- 

 dulär, Excretory and Nervous Systems are of little value 

 in the Identification of species. The Digestive System is of importance, 

 however, because it offers so many landmarks in description. In 

 aU of the species it consists of a mouth perforating the oral sucker, 

 a bulblike muscular pharynx, a short Oesophagus and an intestine 

 consisting of two lateral caeca. 



Reproductive System. This is the most important System 

 of Organs in classifjing the present group of distomes, for the reason 

 that it represents the greatest number of easily recognizable 

 differences. In the development of such a group of closely-related 

 forms, the genital organs, among all the parts of the body, are the 

 ones that have been subject to the greatest Variation. Ovary and 

 testes are, as a rule, easily seen in living or unstained specimens as 

 an irregulär longitudinal series of three brighter spots among bands 

 and streaks of black. The ovary lies just behind the ventral sucker, 

 the first testis behind and on the opposite side of the body, the 

 second testis still farther back and ou the same side as the ovary. 

 Sometimes the ovary is near the middle line and in No. 1 the testes 

 are side by side. The ovary may be compact or lobed and from its 

 inner, posterior end gives origin to the oviduct. Fertilization space 

 and receptaculum seminis are present but there is no Laueer's 

 canal. After receiving the vitelline duct there is an ootype with 

 shell-gland. All of these belong to the first short piece of the 



