70 ILLINOIS BIOLOGICAL MONOGRAPHS [288 



MONOSTOMUM AMIURI Stafford 1900 



This trematode taken from the swim bladder of Amiurus nebulosus by- 

 Stafford, is described by him as follows: "About 5 mm long and 2.25 

 mm broad much flattened and is broadest in its posterior two-thirds, the 

 anterior third narrowing towards the mouth-sucker. The living animals 

 are very soft bodied, inactive creatures." 



"The integument bears a cuticle and is apparently very thin the sub- 

 cuticular and glandular parts seem to have a similar structure to the same 

 parts of the Distomes with which I am most acquainted. The intestinal 

 system begins with the mouth whose thick muscular walls form the oral 

 sucker. Following this is a muscular pharynx and a narrow esophagus 

 which gives rise to two lateral intestinal ceca, extending as broad tubes to 

 near the posterior end of the body where they end blindly." 



"The posterior excretory bladder unpaired." 



"The reproductive system is of the usual complex type. Each individ- 

 ual dioecious. The testes are situated most posterior in the body, between 

 the median expulsion tube of the excretory system and the ends of the 

 intestinal ceca, the vasa efferentia rise out of their anterior ends and 

 proceed, by a direct course, to near the middle of the animal where they 

 meet in the vesicula seminalis. This runs forward and opens by a muscular 

 penis on the ventral surface of the worm, about one-third from its anterior 

 end. The ovary is located a little behind the middle of the animal. The 

 uterus filled with eggs occupies most of the posterior two-thirds of the body 

 and opens by a bulbous vagina immediately behind and to the right of the 

 penis. The two lobular yolk glands lie outside of the forked intestine and 

 extend from the level of the genital openings to the hind end of the animal. 

 A longitudinal yolk duct receives the yolk cells from the numerous follicles 

 on each side and conducts them, by a transverse tube in the region of the 

 ovary, to a yolk reservoir that communicates with the oviduct close by 

 the shell gland. The egg is 45 by 24ju in size and its blunt broader end is 

 provided with a short hooked filament." 



The description and figure of Stafford shows a remarkable similarity 

 to the Heterophyidae with which the worm agrees in having simple sac- 

 like intestinal ceca extending to the posterior end, genital pore in immediate 

 neighborhood of the ventral sucker if that organ is what has been inter- 

 preted as the female genital opening by Stafford. Testes oval, symmetri- 

 cally arranged near the posterior end, seminal vesicle S-shaped, ovary oval, 

 median, anterior to the testes. Vitellaria lateral to the intestinal ceca; 

 extending from the level of the testes. The eggs also fall within the size 

 found in this family but differ in having a short hooked filament at the 

 blunt end. It differs also in that scales have not been recorded for this 

 species by Stafford. 



