282 Henky Leslie Osborn, 



vantageous and a hindrance to the organ in the performance of the 

 function of adhesion. They cannot well be supposed to be of ad- 

 vantage in the performance of that function. At the same time 

 the histological appearance is that of a fullj' equipped sucker. 

 The radial musculature is well developed, and though the organ is 

 of small still it does not appear to have undergone any degenerative 

 changes. If the sucker were not a functional organ we could 

 possible regard the spines as reversionary, since the general cuticle 

 is so spinous and the genital passages are as well. But, though in 

 the living animal, no movements in the ventral sucker were seen 

 we are not justified in assuming that the organ has lost its function, 

 and are left very much in the dark. 



VI. The sub-cuticular cells. 



Students of trematode histology are familiar with the layer 

 of cells which lies directly underneath the cuticula and muscles of 

 the bodywall, and which may be called the sub-cuticular cells. There 

 have been two conflicting opinions as to the origin of these cells. 

 One group of writers, including those who have studied the matter 

 most recently, regard them as parenchyma cells wich have taken 

 up this position parallel with the surface. They believe that the 

 cuticle is the product of their secretory activity. A review of the 

 literature of this subject has been recently given by Pratt (1909) in : 

 The American Naturalist, which may be consulted for furthed details. 

 On the other hand Blochmann (1896), in his theory of the epidermal 

 origin of the cuticle, put forward the hypothesis that the sub- 

 cuticular cells are epidermal cells which have migrated from the 

 surface, descending through the muscle layers, from which point 

 they secrete the cuticula. Blochmann's ingenious view is undoub- 

 tedly more attractive on theoretical grounds, for on the other the 

 cuticula in trematodes and cestodes would be of mesodermal origin 

 unlike that of all other animals, but unfortunately for Blochmann's 

 view it has no observations in its support, and all the observations 

 as to the origin of the cuticula point to its derivation from the 

 fibres of the parenchyma. 



In L. arcanum there is a very definite layer of cells which 

 constitutes a conspicuous zone directly below the bodj^-wall. Fig. 10 

 gives a view of a strip across the body showing this zone in its 

 relation with the body-wall on one side and the deeper parenchyma 

 on the other. The parenchyma here is unusually clear and free 



