16 ILLINOIS BIOLOGICAL MONOGRAPHS [304 



erent from that of any of the members of this family in that it is distinctly 

 divided into uterine duct and uterus-sac as in the Ptychobothriidae. It is true 

 that in the genus Scyphocephalus one or two of the coils of the uterine rosette 

 becomes much enlarged when the organ is filled with eggs, while in Bothridium, 

 as stated by Liihe (1899:49), "Der Uterus bildet keine Rosettenform, lasst 

 jedoch Uteringang und Uterus s. str. deutlich unterscheiden; letzterer stellt 

 gewissermassen eine zweitheilige Uterushohle dar, indem zwei hinter einander 

 gelegene grosse Hohlraume durch einen kurzen und diinnen Canal miteinander 

 in Verbindung stehen." But in neither case is there a single uterus-sac, 

 distinct and separate from the uterine duct or beginning of the uterus, but 

 only a modified rosette formation. Roboz (1882 :2S2) in describing the develop- 

 ment of the uterus oi Bothridium pithonis said that: "In dieser Weise ist er 

 natiirhch nur in jiingeren Gliedern entwickelt, wahrend er dort, wo die Be- 

 fruchtung schon beendet ist, in Folge der immer starkeren Ansammlung von 

 den mit chitinoser Hiille umgebener Eiern immer grosser wird und sich schliess- 

 lich zu einem die ganze Mittelschicht ausfuUenden Sack ausbreitet. " It would 

 thus seem to be comparable to that of the Ptychobothriidae in that its func- 

 tional sac is developed by a distal enlargement of the original duct which grad- 

 ually encroaches upon the medulla, but evidently there is no separation of the 

 organ into two distinct parts at any stage as there is in Haplobothrium. And, 

 as emphasized elsewhere by the writer, this separation is present at all stages 

 in the development of the organ, which as a matter of fact proceeds in quite 

 the same manner as that of Bothriocephalus. In Marsipometra, on the other 

 hand, even tho the sac is formed in the same way, it is never very sharply 

 separated from the uterine duct, altho such appears to be the case in the adult. 

 Reference to the specific description below will elucidate this latter point. 

 Finally as regards the fact that Its eggs are not provided with opercula, Marsi- 

 pometra stands alone. This character would place it at once in the Ptycho- 

 bothriidae, but it is otherwise so closely related to the subfamily Triaenophor- 

 rinae that the family is here emended to accommodate it. Thus it is seen that 

 on account of these two isolated genera the two families Diphyllobothriidae 

 and Ptychobothriidae are much more closely related than was formerly thought 

 to be the case. 



LIGULINAE Liihe 1899 



Scolex unarmed, very short, almost triangular, with anterior end, more or 

 less drawn out into a point according to the state of contraction, passing directly 

 into the chain of proglottides or the similarly shaped imjointed body; surficial 

 bothria small, weakly developed. Neck absent. Formation of proglottides 

 complete, confined to the anterior end or (in young animals) absent. Posterior 

 end rounded. Nervous system distinguished by a large number of plexus- 

 forming longitudinal nerves near both chief strands. Genital organs in sexually 

 mature individuals completely developed close behind the scolex. Genital 

 openings surficial, ventral, lying behind or near one another and near the 

 median line. Testes in a simple dorsal layer in the lateral fields of the medul- 



