3IO R. T. YOUNG. 



engaged, I have examined the reproductive apparatus of a 

 number of species, in one of which I am unable to discover a 

 yolk gland, while in another I find evidence of its degeneration. 

 The species in which this organ is evidently lacking is Thysan- 

 osoma actinoides. A yolk gland in this species was described by 

 Stiles and Hassall in I893. 1 Their work was done, however, on 

 material which they expressly state was in such poor condition 

 that many details could not be worked out. In a study of the 

 reproductive organs in this form Swingle- was unable to find a 

 yolk gland, nor can I do so. Therefore I believe that the former 

 authors were misled, mistaking possibly a posterior lobe of the 

 ovary for a yolk gland. 



In Hymenolepis sp., I find evidence of the degeneration of 



Yolk gland (F) and ovary (0) of Hymenolepis sp. X 500. 



the yolk gland, for here not only is the gland reduced in size, 

 but it contains no yolk. Yolk takes iron haematoxylin w T ith 

 avidity, so that if present in the yolk cells it should appear with 

 this stain, as it does very clearly in the ovary, whose cells are 

 heavily laden with it. In the figure is brought out very clearly 

 the distinction between the yolk filled ova and the empty yolk 

 cells. This is true at least of later stages of the gland. In 

 earlier stages the densely crowded and heavily staining nuclei 



1 Stiles, C. W., and Hassall, A., "A Revision of the Adult Cestodes of Cattle, 

 Sheep and Allied Animals," U. S. Dept. Agric., Bur. An. Ind., Bulletin No. 4. 



2 Swingle, L. D., "The Morphology of the Sheep Tapeworm, Thysanosoma 

 actinoides," University of Wyoming, Agric. Exp. Station, Bulletin No. 102. 



