22 ILLINOIS BIOLOGICAL MONOGRAPHS [372 



large, horseshoe-shaped body, just to the pore side of the median line. 

 Its duct arises from near the median line of the gland. It can be 

 traced inside the gland as an open passage which divides and goes to 

 the two lobes. "When it has emerged from the shell gland the uterine 

 duct passes forward and median with several windings which are fairly- 

 constant in different individuals, to join the uterus near the median 

 line. The uterus is at first a narrow, sinuous transverse tube, just 

 below the upper limit of the ovary and testes. At either end it crosses 

 beyond the excretory ducts ventrally, and turns distad beyond them. 

 Just before the eggs begin to enter the uterus expands considerably. 

 The later development is by outpocketing, the walls of the adjacent 

 pockets touching. The anterior pockets number 28 to 40 being usually 

 about 35 ; the posterior pockets, 22 to 33, being usually about 30. 



The embryo has three membranes. The outer is spherical, 30 to 

 35/x in diameter; the middle is loosefitting and irregular. The embryo 

 itself is 12 to 13/t in diameter. It bears a well developed pyriform 

 apparatus. The dorsal excretory duct lies dorsal of the ventral in 

 young proglottids. As the proglottid ripens it passes laterad and usu- 

 ally ventrad also. At sexual maturity the dorsal duct is usually lateral 

 but it may be both strictly dorsal and strictly lateral in different parts 

 of the same proglottid. The transverse commissure is sinuous. 



The foregoing description, as already stated, is based on well 

 expanded material from central Illinois. In the material from the same 

 localities, however, are a number of very much contracted specimens 

 which are so different from the forms already described that they 

 would no doubt have been classed as separate species if only the pre- 

 served specimens were known. The main differences from the type 

 already described are as follows: 



The length is 30 to 33 mm. The proglottids are all very short and 

 broad. Mature proglottids are 0.325 mm. long by 4.5 mm. broad. The 

 suckers open directly forward. The scolex is half-moon shaped, and is 

 not broader than the first part of the strobila. The genital pore is 

 situated midway on the right margin nearer the dorsal than the ventral 

 surface. The ovary extends from the ventral excretory canal on the 

 pore side to not far from the corresponding canal on the opposite side. 

 The oviduct arises from the median line of the proglottid, half its length 

 lying mediad of the vitelline gland. The transverse commissure of the 

 excretory duct is not sinuous. The dorsal excretory duct is always 

 lateral to the ventral, except in the head region and vicinity. In mak- 

 ing comparisons of these two types, the reader should refer to figures 

 18, 19, 22, and 23. 



