249] NORTH AMERICAN MONOSTOMES 31 



in's Auge, der zur rechten Seite dicht neben und vor dem hinteren Hoden 

 liegt, und an Umfang etwas kleiner als dieser ist. b) Diesem runden 

 Korper hangt zweitens nach. innen ein ovaler, noch kleinerer und ebenfalls 

 weissgelb gefarbter Korper an, der mit ersterem durch einen kurzen, an- 

 fangs weiteren, nachher engeren Kanal in Verbindung steht. c) Endlich 

 liegt drittens, theils unter diesen Organen, theils zwischen dem runden 

 Korper und dem hinteren Hoden eine durchsichtige, fast farbelose und 

 unregelmassig umgranzte, feinzellige Masse, in die der gemeinschaftliche 

 kurze Ovariengang einmundet, und aus der der eierfuhrende Uterus her- 

 vortritt. Es ist mir bis jetzt nicht gelungen, eine Verbindung dieses un- 

 regelmassigen Organes mit dem grosseren runden Korper bestimmt nach- 

 zuweisen; doch bin ich iiberzeugt,. dass eine solche wirklich existirt." 

 Van Beneden (1861) in his study of Monostomum mutabile after character- 

 izing the vitellaria (vitellogene Van Beneden, Ovarien von Siebold) and 

 the ovary (germigene Van Beneden, one of the shell forming organs of von 

 Siebold) says (p. 74), that besides the testes and the ovary only one other 

 organ has been observed by him in the posterior region i.e., the vitelline 

 duct which dilates to form the vitelline reservoir. In regard to the other 

 organs described by von Siebold (1835) he says "Sont-ce la les deux autres 

 organes que M. von Siebold signale et qui contribuent a la formation des 

 oeufs? Cela est probable!" 



More recently Braun (1892) stated that he is able to find the recep- 

 taculum seminis only in Aploblema, Cephalogonimus and in the dis- 

 tomes, and that on the basis of his own research Laurer's canal is wanting 

 in Monostomum mutabile. One year later he states that in the monostomes 

 a Laurer's canal appears to be wanting. Cohn (1902) reported the absence 

 of both these organs in Monostomum oculobium. On the contrary Stossich 

 in the same year after a thorough study of the group confirmed the pre- 

 sence of these organs in several species belonging to at least three genera 

 of this family. Arnsdorff (1908) describes for Monostomum vicarium a 

 small receptaculum seminis. Kossack (1911) after a study of a large 

 number of specimens belonging to different genera of this family, viz: 

 Cyclocoelum, Typhlocoelum, Haematotrephus, Hyptiasmus, states con- 

 trary to the finding of Stossich that both receptaculum seminis and Laurer's 

 canal are wanting in this family. S. J. Johnston (1916) makes no mention 

 of either the receptaculum seminis or Laurer's canal in any one of the 

 three genera studied, Cyclocoelum, Haematotrephus and Hyptiasmus. 



In a study of a considerable number of specimens belonging to several 

 species of the genus Cyclocoelum the writer has observed the presence of 

 the receptaculum seminis. In addition to the observations made on the 

 American material the writer has been given the opportunity through the 

 efforts of Professor Henry B. Ward and the courtesies extended him by the 

 Curators of the museums of Berlin, Gottingen, and Vienna, to study Cyclo- 



