32 ILLINOIS BIOLOGICAL MONOGRAPHS [250 



caelum mutabile, Cyclocoelum problematicum, Cyclocoelum ovopunctatum, 

 Cyclocoelum brazilianum, Cyclocoelum tringae, and Haematotrephus similis. 

 In all of these species a small spherical receptaculum seminis has been 

 found, in position median and dorsal. to the ovary (Figs. 20-24, 26 and 27). 



On the same dorsal level with the receptaculum semnis and posterior 

 to the latter and the ovary one finds the compact shell gland, in size ap- 

 proximately equal to the ovary. It is composed of unicellular glands closely 

 packed together, each of which empties its secretion into the ootype by 

 means of a short straight canal; these ducts form the inner portion of the 

 gland. The ootype in the central portion of this gland gives rise to the 

 uterus which in turn expands, immediately upon emerging, into a large 

 receptaculum semnalis uterinum. During the sexual activity of the worm 

 this pouch is filled with spermatozoa. In the genus Cyclocoelum, the uterus 

 forms relatively short closely packed loops, in general going out from the 

 middle line of the body. Relatively few stretches go directly across the 

 body. The uterus fills out the entire space between the crura, then by a 

 relatively straight stretch it spans the distance to the genital atrium in the 

 region of the pharynx. In lateral extent the uterus reaches in general to 

 the middle or outer wall of the intestine or rarely even out to the body wall, 

 as in Cyclocoelum halli. This species differs in this respect from other 

 species of the genus and according to the generic limits of Kossack does not 

 belong here if this condition is a diagnostic factor. Cyclocoelum halli, 

 however, conforms so closely to the genus in other respects and does not 

 conform to the genus Haematotrephus in that the uterine loops do not 

 bend around the genital organs so that the writer feels justified in placing 

 it in the genus Cyclocoelum. Evidently there is little justification for the 

 creation of a new genus based largely on the extent of the uterus and hence 

 the limits of the genus Cyclocoelum have been extended to include this 

 species. 



The condition known as a situs inversus is a common feature of this 

 family. Looss (1899) asserted that in all forms in which the genital pore 

 is median there is a possibility that sexual amphitypy will occur and 

 suggested that in Monostomes where this is the case situs inversus will 

 probably be found. Cohn (1902) was the first to record this condition 

 in the group when he found in Spaniometra oculobia (Cohn) a situs inversus 

 of the genital glands in a ratio of 9:5. Kossack (1911) added to this by his 

 observations on Cyclocoelum problematicum. Stoss., Cyclocoelum ovopunc- 

 tatum Stoss., and Cyclocoelum vicarium (Arnsd.) in which he says that on 

 the average the right and left positions are equally frequently present. 



The writer has found a similar condition to exist in all species of 

 Cyclocoelum represented in North America as well as being able to verify 

 the observations of Kossack on Cyclocoelum. problematicum and Cyclocoelum 

 ovopunctatum. Reference to the following table shows that the right and 



